by D.P. Mellor
The Optical Panel was able to assist with the production of instruments not directly connected with armaments; for example, lumi-gauge projectors designed to enable the assessment of the accuracy of screw threads and similar mechanisms. These projectors, the optical parts of which were designed in the National Standards Laboratory, were very helpful to makers of machine tools and gauges.
The success of the optical munitions program could never have been achieved without the help of government and university laboratories and departments, whose scientific resources it was the function of the Optical Panel to mobilise. Except in a few instances the laboratories were not involved in large-scale commercial production but this history would not be complete without some reference to them and to the successful way in which they worked together.
Since both the chairman and the secretary of the panel were members of the Department of Natural Philosophy in the University of Melbourne, this automatically came to be regarded as the panel's headquarters. Over many years there had grown up in the University of Melbourne, under Laby's inspiration, a very active school of research with a world-wide reputation. As soon as he became chairman of the Optical Panel, Laby directed that all research except that on optics and related fields should cease, and in this way a large team of physicists, including members of the staff and senior students, was ready to help the panel.
The work undertaken by his department was, like that of the Munitions Supply Laboratories, of an extraordinarily varied character. Being the headquarters of the panel, it was closely involved in a great deal of advisory work for contracting firms, for the Services, and for the panel itself. Small orders were accepted and executed for such specialised instruments as introscopes, spherometers, stereoscopes and telemicroscopes. It is in fact difficult to single out any activity as representing the labora tory's most important contribution. Not only did the members of the laboratory design and produce the prototypes of a great variety of instruments, they also undertook the analysis and testing of instruments and tropic proofing. When Army Inspection became anxious to have all the optical parts of dial sights thoroughly tested, the members of the laboratory staff devised special methods based on interferometry for this purpose.
At the time when optical glass was very scarce and thousands of prisms were needed for tank periscopes, a technique for welding plate (crystalex) glass into solid blocks was worked out. Fortunately extensive use of this improvisation was not necessary because optical glass became available soon afterwards. An important use was, however, found for crystalex glass in Mosquito bombers: selected areas of the glass were sufficiently flat and homogeneous for use as windows through which aerial photographs might be taken.
An interesting process developed at the University of Melbourne was that of making mirrors by depositing films of aluminium on glass. The technique was not new: it had in fact been invented in the late 1930's by Dr John Strong of the California Institute of Technology, who used it in making reflectors for astronomical telescopes such as the 100-inch instrument at Mount Wilson and later the 200-inch telescope at Mount Palomar (California). Previously, metal reflecting films on glass had always been prepared by the chemical deposition of silver from aqueous solutions. Although the silvering process was not difficult to carry out, the resulting film suffered from a number of serious disadvantages in so far as it was soft and easily scratched and also highly susceptible to tarnishing. Deposition of a film of aluminium was more difficult because it had to be carried out under more exacting conditions in a high vacuum (less than one ten-thousandth of a millimetre of mercury). The object to be coated was placed in a specially built tank. The largest used in Melbourne was 40 inches in diameter. At some distance above the surface to be covered were placed a number of tungsten filaments that had been coated with aluminium. After the tank had been thoroughly evacuated by means of oil diffusion pumps, the tungsten filament was heated electrically to a sufficiently high temperature to melt and ultimately vaporise the aluminium. Atoms of aluminium were shot out from the heated filaments across the intervening vacuum, and if the filaments were correctly placed, deposited in an even, shining film on the surface being coated.
If it was necessary to make a mirror with a metal film on the front instead of on the back, aluminium became the metal of choice because its resistance to tarnishing was so much greater than that of silver. Exactly this situation arose when several thousand universal stereoscopes and hinged sighting telescopes had to be fitted with reflectors. These instruments were needed urgently, the stereoscopes for viewing aerial photographs and the hinged telescopes for use in tanks. The hinged telescope was designed for seeing round corners, a feat achieved by means of aluminised mirrors. Practically all the aluminium-coated mirrors needed were made in the Department of Natural Philosophy of the University of Melbourne.
Another important activity of the University of Melbourne was one in which the Departments of Botany and Chemistry collaborated with the Department of Natural Philosophy. This was a problem of making graticules, which were required for practically every optical instrument used in the Services, except the signalling telescope. A graticule was a glass disc on which were inscribed measuring marks or scales to assist in the determination of the size, distance, direction or position of a distant object. It was so placed in an optical instrument that the scale marks and the object were seen simultaneously.
Making a graticule involved two main operations. First was the preparation of a blank disc of glass with a highly polished surface free from all imperfections such as pits and scratches. It took some time to convince the firms producing these blanks of the high degree of perfection of surface needed for this work. After many failures both the Australian and British Optical Companies succeeded in making satisfactory discs in large numbers. The second operation was to inscribe the scale marks on the disc. This was done first by covering the disc with a layer of impervious material such as bitumen. With the help of a pantograph, the scale was next drawn by cutting through the bitumen layer with a fine chromium-plated gramophone needle, so exposing the underlying glass for subsequent etching with hydrofluoric acid. On completing the etching, the bitumen layer was removed and the lines filled in by rubbing in printer's ink. This method, and also direct ruling with a diamond tool, was used at the Munitions Supply Laboratories.
When the output of optical instruments increased rapidly, as it did early in 1942, these methods of production were too slow to keep up with demand. It was about this time that Professors Agar [39], Hartung and Turner [40], seeking ways in which they could help with war work, visited the Superintendent of the Munitions Supply Laboratories to discuss plans a graticule annexe at the university. From the discussion it was clear that some of the strain on the Supply Laboratories could be relieved the establishment of an annexe, and steps were immediately taken to set one up in the laboratories of the Department of Botany.
At first graticules were made by the usual etching process, but while this was going on Hartung set about devising a photographic method of putting scale marks on glass. This he did with considerable success by simplifying the fish glue-lead sulphide process worked out by the British Scentific Research Association. This process had the advantages of speed and accuracy as well as of avoiding etch marks and other damage to the glass surface incurred by the usual method, and these outweighed disadvantages, such as poor resistance of the graticule to abrasion and its liability to deterioration in the tropics. Graticules intended for use the tropics were given special proofing treatment which rendered them quite resistant. Official approval of the photographic method was given by the Chief Military Adviser in March 1942. By November 1944 the Botany annexe had completed over 20,000 graticules of 60 different types, including those for binoculars being reconditioned in Sydney and Perth, and an order for 188 binocular graticules for the United States Army had been filled.
It must not be thought that the work of the cooperating laboratories was an unbroken record of successes unalloyed with disappointments and unrewarded effort. One difficult instrument whose construction was under taken by the Department of Natural Philosophy was the Height and Range Finder No. 3, Mark IV. On learning from army authorities that some 65 of these instruments were needed, a team of physicists under the leadership of Associate Professor Martin [41] set out to build a prototype instrument. No drawings of the instrument were available, and only after long hours had been spent on an analysis of an instrument lent by the army were the intricacies of its gears and mechanical parts analysed. When, in August 1941, the first instrument was almost complete, the army cancelled the whole order. Referring to this some time afterwards, the secretary of the panel wrote: "It was extremely disappointing to this laboratory to find that, after such extensive work, all its efforts were of little avail. There was one consolation - the stand of the prototype was used by the army to replace a broken one. It is, however, very difficult to expect continued zealous work by a laboratory when it learns that, after months of work, all effort has been wasted."
On this, the responsible army authorities, who, it should be said,
had a very high regard for the work of the Optical Panel, took a
different point of view. The course and needs of a war were governed by
the action and reaction of two opposing sides, and it was in relation
to only one of these that any kind of forecast could be made. War was
inherently a wasteful process; every soldier was constantly engaged on
difficult, exhausting and often dangerous activities that proved to be
fruitless. Probably as much as 90 per cent of a soldier's time was
spent in preparation for something that never happened. This being so,
scientists had also to be prepared to find some waste in their own
efforts, even in the best organised supply systems.
With a background of experience developed slowly over the pre-war years, the Optics Section of the Munitions Supply Laboratories served as the most important centre for the diffusion of optical techniques among contracting firms. A team of experts for computing optical designs was built up and on many occasions these scientists, together with skilled technicians, were lent to contracting firms for months at a time. The section had facilities for making and testing practically every type of optical instrument, and the range of work covered was much greater than in any other Australian establishment. A prototype of every optical instrument made in Australia during the war was thoroughly tested at Maribyrnong.
Before an instrument was passed over to the Services it was thoroughly inspected in a last effort to ensure that it would do what was intended of it. Because optical munitions had never before been made in Australia, many difficulties not met in other fields were experienced in maintaining satisfactory inspection. There were not enough men qualified to do the work until the Munitions Supply Laboratories began training additional army inspectors. Training alone did not solve all the problems of inspection, since doubts sometimes arose over the interpretation of specifications and requirements.
As the basis for his examination of an instrument, an inspector had
the specifications which had been drawn up for it, and it was his
business to see that the instrument had been constructed in accordance
with these specifications. However carefully written, specifications
occasionally left something to the judgment of an inspector. For
example, a lens was often specified to be made of glass reasonably free
from seed (air bubbles) but no explanation was given of what was meant
by "reasonably free". Further more, some requirements, such as the
definition of a telescope, were a matter of subjective judgment. The
Optical Panel occasionally intervened when there was evidence that
inspection was either not exacting enough or too exacting. On one
occasion army inspectors rejected 400 prisms on the ground that they
showed tiny scratch marks and chips. The panel set up a special
inspection committee to look into this matter. After conducting careful
experiments on the performance of the rejected prisms, the committee
came to the conclusion that the rejections were unwarranted because
when mounted into instruments the prisms gave excellent service. When
delivering its judgment the committee observed that "while the makers
of optics should endeavour to produce them free from minor defects, no
optics should be rejected for a defect which in no way detracted from
its performance". Difficulties of this kind were usually obviated by
the simple device of supplying the inspectors with approved samples of
lenes, prisms or complete instruments so that they might have a basis
for comparison.
AIthough it is at first surprising to find the Commonwealth Solar Observatory entering the field of munitions manufacture, the connection is quite simple: one of the main preoccupations of astronomers was with telescopes, and although they did not usually build their own instruments they necessarily knew a good deal about them and their operation; as already mentioned, nearly all optical munitions contained telescopes.
At the suggestion of the director, Dr Woolley, and with the consent of the Minister for the Interior, the observatory ceased practically all peacetime activities in July 1940 and devoted its resources to making optical munitions. Additional buildings, some of them air-conditioned, were erected and machine tools provided under the Lend-Lease program were installed [42]. With the machinery tools the observatory built its own glass-working machinery. At the peak of its activity some sixty persons were employed, which meant a big expansion of the small community that had made up the pre-war observatory.
All the grinding and polishing machines used were designed in the
observatory and made either in its own workshop or in the Department of
the Interior workshop in Canberra. Contracts for the production of
eleven different instruments were completed. The observatory ranked
with the Supply Laboratories and the University of Melbourne as a
centre for pioneering optical techniques and for diffusing them to
industry. Representatives of most of the firms that became engaged in
optical manufacture visited Mount Stromlo at some time.
Much of the work of the Physics Section of the National Standards Laboratory related to the study of the absorption of ultraviolet, infra-red and ordinary light by glasses of all kinds.
It had long been known that observations of an eclipse of the sun made without smoked glass or other suitable moderating glasses could produce serious and often permanent damage to the eyes, known as eclipse blindness. Since eclipses of the sun are fairly rare occurrences, comparatively little attention had been paid to the nature and cause of eclipse blindness, but when anti-aircraft gunners in the brilliant sunshine of the deserts of the Middle East and the tropical regions of the Pacific were forced to look into the sun to observe dive-bombing aircraft, the complaint became of wider interest, this time under the name of anti-aircraft spotters' retinitis. From both these regions came reports of serious injuries to the eyes of anti-aircraft gunners, resulting in permanent blindness [43]. Though these reports were not numerous they were sufficiently serious to cause investigations to be made.
Experiments carried out many years ago [44] on the eyes of rabbits and monkeys led to the belief that damage was caused by overheating of the retina, the region in the back of the eye on which the image is formed. These findings were confirmed at the Kanematsu Institute in Sydney, where a extensive series of experiments was made on rabbits [45]. Briggs and Giovanelli of the National Standards Laboratory then began to study the physical aspects of the problem with the object of finding out what rise in the temperature of the retina could be expected [46]. Calculations based on mathematical formulae developed by Dr Jaeger [47] and Professor Carslaw [48], who some years before had made a special study of the conduction of heat, led them to the following conclusions: that the visible and infra-red light from the sun were about equally responsible for the temperature rise of the retina; and that the rate of the temperature rise was very rapid - practically the whole rise (95 per cent of it) occurring within half a second.
Having established these facts they set about devising suitable goggles using tinted, infra-red-absorbing glass. The "lenses" of the goggles were flat pieces of glass of the kind used in welders' goggles. In this there was of course nothing new. The novelty they introduced was to place in the centre of each lens two small thick discs of very dark welders' glass fused on to the main disc by an ingenious process developed and patented by the Council for Scientific and Industrial Research [49]. These discs, of just the right size to block out the sun, reduced the light reaching the eye to about one-millionth of that which would otherwise reach it, so that one could look through the disc directly at the sun and see it at the same brightness as the rest of the sky. Under these conditions it was quite easy to see a plane silhouetted against the sun. These goggles, when tested in experiments carried out in conjunction with anti-aircraft defences, Sydney, in which a dive bomber attacked from the sun, were found to improve the efficiency of members of the gun crew. The goggles were adopted first by the navy and later by the other two Services.
Physical problems relating to "dark adaptation" by gunners and pilots were also studied in the Physics Section [50] The problems encountered were of two main kinds. First there was the problem of how to reduce eye fatigue of pilots flying at night and forced to read the blue self-luminous dials of the instruments on their control panels. A group of Catalina flying-boats based on Cairns used to make regular flights known as the "milk run" to the north over Rabaul and its surrounding territory; the flights lasted twenty-four hours. Reports came in of severe fatigue experienced during these long flights, some of it doubtless due to eye strain, and it was clear that anything at all that could be done to reduce the strain would be well worth while. A second, closely related problem, was to accustom the eyes rapidly to seeing in the dark. Anyone who has gone from sunlight into a darkened room will recall the difficulty experienced at first in finding the way round. After twenty minutes or so the eyes become dark-adapted and it is then much easier to see in dim light. In the operations of war there were a number of situations in which it was necessary for the eyes to adjust themselves rapidly to a dim light: a night pilot had to look from the light of his cockpit to the outside darkness and do his best to spot the enemy; men on a ship in their lighted quarters, due to go on duty on the bridge or called suddenly to action stations in the dark had an advantage if they were immediately able to see in the dark to their maximum ability. In both cases it would obviously be impossible, or very inconvenient, to wait twenty minutes for the eyes to adapt themselves.
Early in 1940 Dr V.D. Solandt and Dr C. H. Best (one of the co- discoverers of insulin) found that a person's eyes could be adapted to seeing in the dark by his remaining in a room illuminated quite brightly with red light for about thirty minutes [51]. The first application of this fact seems to have been made in Canada in December 1940 when night trials were carried out in R.C.A.F. aircraft under the direction of Wing-Commander T.R. Loudon. This led to the practice of night-fighter pilots' wearing red goggles while they were standing by for emergencies.
The explanation of the usefulness of red light for this purpose rests on the fact that the retina of the human eye contains two kinds of light sensitive elements: the cones, which operate in bright light and are responsible for colour vision, and the rods, which provide the special sensitive elements for seeing in dim light where their excitation yields only sensations of neutral grey. The rods contain a pigment known as visual purple, and it is the absorption of weak light by this pigment that makes the rods light-sensitive. In bright white light, however, visual purple is bleached, and the rods cannot function. By resting in the dark visual purple is regenerated in the rods and in this way ability to see in a dim light may be restored. Although bright white light bleaches visual purple, red light of the right wavelength has little effect on it. Hence, by wearing red goggles in a room illuminated with ordinary white light or daylight, a person can become dark adapted. The glass of the goggles must be of such a shade of red that it will admit light without affecting the rods. The Physics Section drew up the specifications for such a glass, which was subsequently made by Australian Window Glass Pty Ltd.
The problem of how best to illuminate the control panels in the cock pits of night-flying aircraft was solved by using the same kind of light as was needed for dark adaptation. Early in the war aircraft instrument dials were marked with a self-luminous paint excited to a blue phosphorescence by the addition of traces of radium or mesothorium. This faint blue light was the worst kind of light under the circumstances, because with it sharp vision was impossible. To understand the usefulness of red light in reducing eye fatigue in night pilots it is necessary to consider in a little more detail the structure of the retina, the light-sensitive portion of the eye.
Detailed study of retina shows that clusters of rods (the dim-light, sensitive elements) are connected to the brain by one nerve fibre; cones near the centre of the retina are connected individually to the brain. Rods therefore transmit a rather fuzzy stimulus to the brain and sharpness of vision or detailed vision is not possible in a dim light. Visual acuteness is achieved in bright light by means of the small central area of the retina, known as the fovea. The fovea includes what is called the fixation point of the eye. To look directly at something is to turn one's eyes so that its image falls on the fovea, a small area no bigger than a pin's head in which only cones are to be found. Rods and cones are sensitive in varying degree to light of all colours, but the cones are more sensitive to red than the rods [52]. Light from blue self-luminous radium paints is insufficiently intense to excite the cones appreciably, and although it does excite the peripheral rods distinct and sharp vision is unattainable because of the way the Iods are linked up to the brain. On the other hand, a sufficiently bright red light stimulates the cones and when it is focused on the fovea clear and sharp images are formed. At the same time the red light has relatively little effect on the rods and therefore does not hinder dark adaptation of the eye.
These, then, were the reasons why cockpits of Beaufort bombers and
Catalina flying-boats were adapted to the red floodlighting system.
Special cockpit lamps were designed and photometers made for measuring
the in tensity of the red illumination. Because it was necessary to
ensure that pilots would be able to adjust the brightness levels
sufficiently to cope with a wide range of light outside the aircraft,
which of course varied according as it was dawn, dusk, full moonlight,
starlight or a very dark night, extensive studies were also made of
factors affecting dark adaptation of the eye under all conditions.
Crews of the Catalina flying-boats were enthusiastic in their praise of
the improvements brought about by the changeover to the system of red
flood-lighting. Another solution to the same problem, successfully
developed overseas, was to use self-luminous paint so compounded as to
luminesce an orange-red colour. Instrument dials marked with this
luminous paint were reasonably easy to read and the light had the
virtue of being independent of electric batteries.
The most creditable achievement of the University of Sydney in the field of optical munitions was the production of the ring-sight telescope, an instrument given high priority in the list of army requirements. Its construction was planned as an insurance against the possible failure of the program of work on electrical predictors undertaken independently of the Optical Panel. The contract was given to the University of Sydney because no commercial firm would undertake it; the work was very intricate, and the number required - 85 - made mass production impracticable. This was the only instance of a university becoming a major contractor for the manufacture of a large and complicated instrument.
The ring-sight telescope was an accessory of anti-aircraft guns and was in the nature of an optical predictor, an instrument which when trained on a moving target indicated (at least in theory) to the gun crew the correct point of aim and fuse setting to cause a shell to explode on the target. It was described by Professor Vonwiller as being mechanically and optically one of the most complicated of military instruments, including twenty-eight lenses and prisms and several intricate moving parts. Since none of the experts at Maribyrnong or at any of the other cooperating laboratories had had any experience with this kind of instrument, the university was thrown on its own resources.
It experienced all the inevitable setbacks of wartime: materials that were slow to arrive, and sub-contractors who failed to complete their tasks on time because of shortage of machine tools, and for other reasons. In an effort to speed up work at the university, working hours were increased to sixty-two a week, in some instances with disastrous results; several members of the staff, who were carrying on their normal teaching work at the same time, broke down in health and there was a general loss of efficiency. The team at length triumphed over all its difficulties and instruments were produced at a rate well ahead of the guns with which they were to be used. Then came a disappointment similar to that experienced by the workers at Melbourne University. When scarcely more than half the instruments had been completed word came through that no more were required. By 1944 the Japanese had been defeated in the air, and few anti-aircraft guns were needed. Some, at least, of the instruments were used and to good purpose. Reports came back from New Guinea that the ring-sight telescope was, because of its lightness and compactness, successfully used in the jungle where it would have been quite impracticable to use heavy electrical predictors weighing some tons.
Among other tasks successfully accomplished at the University of Sydney, the most notable was the reconditioning of about 10,000 binoculars that had been called in from the public. The binoculars were fitted with graticules and the two telescopes of which they are composed were accurately aligned. This adjustment had to be made in the majority of the instruments. Unless the two parts were strictly parallel, eyestrain was likely to result from their continuous use. Mr G.A. Harle devised a special arrangement for rapidly making the axes of binocular telescopes parallel, but even with this aid many people had to be employed on the work. At the height of its activities the Physics Department employed about 140 workers, mainly women and girls, most of whom were engaged in reconditioning binoculars.
The University of Sydney was the main centre for the development of a process known as blooming, a method of treating glass surfaces to increase the amount of light passing through the glass by reducing losses by reflection. The importance of the process was that it could be used to increase the performance of an optical instrument in poor light. Telescopes had occasionally to be used in the early dawn, a period of great danger on land or sea because of enemy approaches during the hours of darkness. An aerial photograph might have to be taken under similar adverse conditions. It was therefore important to ensure that the telescope or camera transmitted as nearly as possible all the light reaching it.
As long ago as 1892, Mr H.D. Taylor, an English lens expert, discovered that a photographic lens which had become accidentally tarnished and apparently spoiled gave a much better performance than an untarnished lens in that it transmitted more light. The cause of this was not understood until 1935, when J.H. Strong and other American workers correctly attributed it to a thin film of transparent material on the glass surface. Optical theory showed that if a glass surface was coated with a transparent film of a thickness equal to one quarter of the wavelength of light, and if the film's index of refraction was equal to the square root of the index of refraction of the glass, all the light falling on the glass passed through it and none was lost by refiection. For several reasons these conditions could not be fully satisfied. The required film thickness varied with the wavelength of light used; white light covered quite a wide range of wavelengths. The refractive index of all known materials suitable for forming films was in every instance greater than the desirable value, but with a fairly close approach to this value reflection could be considerably reduced in the spectral region to which the eye was most sensitive (the green-yellow region).
The process of depositing a hard, transparent and adherent thin film on glass was quite a straightforward one, but it had to be carried out in a very high vacuum. The material from which the film was formed depended on the nature of the underlying glass. Magnesium fluoride, one of the substances extensively used for this purpose, required a high temperature to cause it to evaporate. It was therefore placed in a small electrically-heated molybdenum boat above which, and at some distance, was suspended the glass object whose surface was to be coated. The whole arrangement was covered with a large glass bell jar from which air was then completely withdrawn by means of powerful high-vacuum pumps. Control of the thickness of the film deposited was achieved by noting the time for which it was allowed to grow. Only very thin films of the order of a few hundred thousandths of an inch were required. A rough idea of their thickness could be gained by observing the interference colours of the films when illuminated with white light.
With an untreated lens the loss of light by reflection was between 4 and 6 per cent, depending on the kind of glass. In a complete optical instrument this loss occurred at each glass surface, so that the ring-sight telescope with its twenty-two glass surfaces transmitted only about one quarter of the light reaching the objective of the instrument. Dr Bannon [53], who developed the blooming process at Sydney, was able at an early stage of his work to increase the light transmitted by the ring-sight telescope from 27 to 47 per cent, and that of binoculars from 50 to 75 per cent. Later work gave even better results but came too late to have any real usefulness during the war. The results afford, however, some idea of the proficiency with which this technique was developed. The laboratories at Hobart and Maribyrnong took up the process later, and in the immediate post-war years much use was made of it, particularly at Hobart, in treating lenses of aerial and cinematograph cameras.
The University of Sydney served as a centre for the dissemination of
a knowledge of the principles of optical design, and special lecture
courses on geometrical optics were given by Esserman, Vonwiller and
Harle.
In Tasmania, Professor McAulay [54] took up the work on optical munitions with enthusiasm and in a very short time spherical and flat surfaces were being worked in the laboratory by members of his staff and senior students. In this development he was helped by Mr Waterworth [55], a man of considerable ingenuity and mechanical skill, and Mr Cruickshank [56], whose work in optics led to useful original contributions to that subject.
At one of the early meetings of the Optical Panel, the question of making glass prisms came up for discussion. It had been realised earlier that making prisms would present difficulties, and at first it was hoped to avoid them by using aluminised mirrors as substitutes. McAulay's group however accepted the challenge and began work immediately. The difficulties inherent in making prisms may be gathered from the fact that the surfaces of prisms must be optically flat - that is, level to within about one-millionth part of an inch - and the angles between the surfaces must, in the most exacting instance, be accurate to within a few seconds of arc. To achieve this degree of accuracy Waterworth designed a number of ingenious jigs, which located prism blanks so accurately that relatively little skill was demanded of the operator. Waterworth's method of doing this was novel and did much to make possible Hobart's extraordinary output of prisms. All the machinery used in the specially constructed Optical Annexe built for the Commonwealth Government in the grounds of the university was designed and made in Hobart.
It was not long before they were able to produce satisfactory prisms of all kinds: prisms for range finders, periscopes, aerial cameras and many other instruments. The staff of the annexe grew from 6 to 200 within a year, the new recruits being mostly untrained girls. In its four years of operation the annexe turned out some 14,000 prisms, valued at about £250,000. The high optical standard of this work was attested by the Physics Department of the University of Melbourne, where exacting interferometric tests capable of revealing the most minute optical imperfections were made on the prisms.
During a visit to the United States in 1942 Hartnett, finding that country very short of prisms, arranged for a shipment of about 7,000 roof prisms made mainly in Hobart to be sent to the Frankford Arsenal. Not withstanding the fact that the standards of inspection there were most rigorous, the prisms were favourably received.
One of the outstanding achievements of the Hobart Annexe was the
designing and making of aircraft camera lenses. In face of great
difficulties, such as inadequate testing equipment, glass and machine
tools, and the inability to obtain adequate and continuous funds for
development work, the annexe succeeded in making more than 100 lenses
for the R.A.A.F. At no time was optical glass of the required type
available for the manufacture of aircraft lenses of standard designs;
each type of lens had to be redesigned to permit the use of those
glasses that were at hand. Such difficulties were rapidly overcome. For
example, in the short time of six weeks a lens with a focal length of
36 inches was designed and made, and by means of aerial photographs was
shown to compare very favourably with a British lens of the same focal
length. It was later sent to the British Admiralty for report, and
found to be only slightly inferior to later British models. While
developing methods for making camera lenses at Hobart, McAulay and
Cruickshank worked out important and entirely new methods for
calculating lens shapes, details of which were not published until
after the war. Their methods of computing the effect of small changes
in the dimensions of a lens on the formation of an optical image, were
taken up by oversea optical firms.
In every optical instrument for measuring or fixing direction with
regard to the horizontal - in gunsights of all kinds, height, range and
position finders, and director telescopes, to name only a few - a
spirit level or bubble was needed to define the horizontal plane or
vertical direction. Bubbles of this kind had not previously been made
in Australia, and at the beginning of the optical munitions program an
urgent need for them arose. At the instigation of the
Directorate of Ordnance Production, Kerr Grant, Professor of Physics in the University
of Adelaide, undertook their production. A satisfactory technique for
making bubbles was devised by Mr H. R. Oliphant, a technician in the
Physics Department. It was soon shown that there were no technical
difficulties in the way of manufacturing spirit levels in Australia,
and in a short time details of the technique were handed over to Claude
Neon Lights Ltd and the Precision Glass Instrument Company, both of
Victoria. Before June 1941 some 4,000 of every type needed for optical
munitions had been produced. After that, bubbles were made at the rate
of 10,000 a year by amazingly simple methods. Some of the bubbles were
extremely sensitive, being capable of detecting a slope of one inch in
three miles and a half [57].
In spite of its great distance from the industrial centres of the
eastern States and the difficulties of communication, the Physics
Department of the University of Western Australia, under Professor
Ross, did its share of work in optical munitions. It reconditioned and
tropic-proofed a large number of binoculars, assembled and repaired
many instruments, and made graticules and test plates.
Except for work on tropic-proofing, the greater part of the optical munitions program was completed by the end of 1943. Many of the later meetings of the panel were therefore devoted to discussions on the fate of the optical industry after the war. The panel was unanimous on the need for maintaining training and research in both pure and applied optics, and it set out in detail schemes for the training of physicists in what it regarded as the most appropriate universities for this work, namely Tasmania, Melbourne and Sydney.
On 6th December 1945, when it seemed to have fulfilled its purpose
and was no longer able to find useful activity, the panel was
dissolved. Whatever the shortcomings of its constitution - the panel had
its critics - it had done a fine piece of work and had gained the
confidence of the army as few other scientific bodies had done. All the
instruments the three Services had asked for had been produced. The
panel was fortunate in having as its chairman (from its inception to
March 1944) Professor Laby, one of Australia's outstanding physicists.
Throughout his scientific career Laby proved himself an experimenter of
the first order. His work on the precise determination of the
mechanical equivalent of heat became a classic in this branch of
physics. He had an abiding passion for accurate measurement, which
further displayed itself in his work on the charge of an electron. One
of his colleagues said of him: "No physicist had a greater respect for
precision, and his genius lay in a capacity to design an experiment to
achieve it."
Towards the end of 1943 the Commonwealth Government set up the Secondary Industries Commission for the purpose of investigating methods of ensuring a smooth transition of war industries to a peacetime basis [58]. To assist the commission a number of advisory panels were formed. Among them was the Optical Industry Advisory Panel, the members of which were recruited from the Scientific Instruments and Optical Panel. The terms of reference of the Advisory Panel were to consider:
The panel went into these questions at great length and made a number of recommendations to the Secondary Industries Commission. For example, it strongly recommended that the Commonwealth Government should make available a sum of money for experimental work on optical glass to be made in small platinum pots. It also recommended that every effort should be made to put the optical industry on a commercial basis after the war. The Secondary Industries Commission, convinced that the economic future of the optical industry was too insecure and that the possible market for each of many types of instrument was far too small, decided that it could not recommend to the Government any of the proposals made by the Optical Industry Advisory Panel, not even the one dealing with provision of money to support small-scale experimental work on optical glass. This decision put an end, for some years at least, to any hope that a rationalised commercial optical industry might be developed with the help of the Commonwealth Government. All that remained of the wartime optical industry was the annexe at Hobart, which the Commonwealth Government sold to Waterworth. Here the successful production of film-strip projectors, lenses and prisms was in 1955 still being carried on though with increasing difficulty because of rising costs [59]. Up to this time nothing had been done either by government or private research laboratories to revive work on optical glass, even on a small scale, by using platinum pots as had been recommended by the Optical Advisory Panel. At this period important advances were being made in optical glass overseas. New and extraordinary types of high refractive index glass for aerial camera lenses were being developed. Ironically enough, one of the most notable developments in 1955 was the manufacture of glass on a commercial scale in large platinum pots, thereby greatly increasing the yield of glass from below 20 to over 70 per cent.
The problem of keeping up to date in the optical industry was of course not peculiar to Australia. It arose even in the United States, the most highly industrialised of nations. There as elsewhere the peacetime annual requirements of precision optical instruments were small compared with wartime demands, and much thought was given to the problem of keeping abreast of scientific progress made in the laboratory. The advice given by Condon applied equally well to Australia:
If we are to be again prepared for future emergencies, a program of research and experimentation must be maintained. Stockpiling of optical glasses is not a solution, for stockpiling tends to maintain the status quo, saddling the military services with obsolete instruments and making the introduction of better glasses and instruments difficult. As a general rule, with valid exceptions only in the case of basic raw materials, stockpiling is futile and tends to hinder progress. The only sensible solution is a progressive research program involving the new type of optical glass, analysis of the physics and chemistry of optical glasses and development of new and more efficient methods of processing optical glass.[60]
Failure to follow up in any way the wartime successes with optical glass in Australia was the darker side of the picture; on the brighter side was the work of the university departments of physics (especially that of Tasmania) and government laboratories. Often considerably helped in the immediate post-war years by equipment and materials acquired through the Disposals Commission, these laboratories continued to prosecute research on optics and optical instruments so that at least the scientific basis for an emergency optical industry was encouraged and developed.
[39] W.E. Agar, CBE; FRS, MA, DSc.
(Served Highland Light lnf 1914-l8.) Prof of Zoology, Univ of Melb,
1920-48. B. Wimbledon, Eng, 27 Apr 1882. Died 14 Jul 1951.
[40] J.S. Turner, MA, PhD, MSc. Prof
of Botany and Plant Physiology, Univ of Melb, since 1938. B.
Middlesborough, Eng, 9 Sep 1908.
[41] Sir Leslie Martin, CBE; PhD.
Assoc Prof of Natural Philosophy, Univ of Melb, 1937-45, Prof of
Physics since 1945. Chairman, Defence Research and Develop Policy,
since 1945. Of Kew, Vic; b. Melbourne, 21 Dec 1900.
[42] By the end of the war, Dr
Woolley considered, the observatory was equipped as well as, if not
better than, the Royal Observatory at Greenwich. This no doubt
influenced the Universities of Yale, Columbia and Uppsala when in 1950
they decided to establish an observatory on the slopes of Mount
Stromlo. Unfortunately some of this equipment was destroyed in a bush
fire during the summer of 1951.
[43] James Flynn (Surg Lt-Cdr),
"Photo-retinitis in Anti-aircraft Lookouts". Medical Journal of
Aust (1942), p. 400
[44] F.H. Verhoeff and L. Bell, "The
Pathological Effects of Radiant Energy on the Eye". Proceedings
American Academy of Arts and Science, Vol. 51 (1916), p. 630.
[45] J.C. Eccles and J. Flynn,
"Experimental Photo-retinitis", Medical Journal of Aust, Vol. 20
(1944), p. 339.
[46] G.H. Briggs and R.G. Giovanelli,
National Standards Laboratory Report PSS. 8 (March 1943).
[47] J.C. Jaeger, MA, DSc. Lecturer
in Mathematics, Univ of Tasmania; Research Officer Radiophysics
Laboratory CSIR, Prof of Geophysics, Aust National Univ, since 1952. Of
Hobart; b. Sydney, 30 July 1907.
[48] H.S. Carslaw, DSc. Prof of
Mathematics, Univ of Sydney, 1903-35. B. Helensburgh, Scotland, 12 Feb
1870. Died 11 Nov 1954.
[49] Australian Patent Application
No. 11216/43.
[50] This work was done by a team
under the leadership of Dr G.H. Briggs, the Officer-in-Charge of the
section, and included R.G. Giovanelli, E.H. Mercer and FO C.J.
Mathieson.
[51] W. Eggleston Scientists at War
(1950), p. 247.
[52] The spectral response curves of
the two are well known: the maximum sensitivity of cones occurs at a
wavelength of 5550A and that of the rods at 5050A.
[53] J. Bannon, DSc. Research officer
Radio Research Board 1938-42; C'wealth Research Fellow 1942-45; Lecturer
in Physics, Univ of Sydney, since 1946. Of Sydney; b. Ireland, 16 Sept
1900.
[54] A.L. McAulay, MA, BSc, PhD. Prof of
Physics, Univ of Tasmania, since 1927. B. Hobart, 15 Nov 1895.
[55] E.N. Waterworth. Instrument maker;
of Hobart; b. Hobart, 15 May 1905.
[56] P.D. Cruickshank, DSc. Assoc Prof
of Physics, Univ of Tasmania, since 1949. B. Hobart, 3 Jul 1908.
[57] Kerr Grant, "The Making of
'Bubbles' for Spirit Levels". Australian Journal of Science,
Vol. 3 (1941), p. 147.
[58] The commission
had its first meeting on 15 Nov 1943. Its members were: J.K. Jensen,
Secretary, Dept of Munitions (Chairman); D.J. Nolan, Chairman,
Standing Committee of Allied Supply Council; E.T. Merrett, Director of
Small Craft Construction, Dept of Munitions; W.D. Scott, Finance
Member, Board of Area Management; S.F. Cochran, Chairman, State
Electricity Commission of Queensland.
[59] A scheme for making microscopes
for students was completed. but not by private industry. As originally
planned, the lenses were made by the Munitions Supply Laboratories, and
owing to the failure of a private firm to complete the order for stands
the Munitions Supply Laboratories finally made the whole instrument. In
all some 500 microscopes were supplied to the Universities Commission.
[60] E.U. Condon, "Science and the
National Welfare",Science, Vol. 107 (1948), p. 5.