90 



NATURE 



[May^ 



1903 



hand, and that done by our manufacturers, which has, so 

 far, succeeded in keeping them in the van of progress, in- 

 vestigations into the underlying facts of photography may 

 be said to be non-existent in this country. A thousand 

 pounds is a very modest sum to ask for, though no doubt 

 it will serve to make a beginning. We hope that before 

 very long this sum will be multiplied many times over, and 

 that the science of photography will begin to take its proper 

 place, instead of being regarded, as it is too often at 

 present, as a very minor detail of a considerable industry, 

 and an empirical art. The following remarks are from 

 Sir William Abney's address : — 



Looking back to the first day of this Society's exist- 

 ence, one is forcibly reminded of the advances that have 

 been made, not only in the science, but in the art of 

 photography, but these advances I think might have been 

 more rapid. A very brief comparison of the processes 

 existing now and fifty years ago will show what I mean. 

 Paper processes, founded on the original process of Fox 

 Talbot, were well to the fore fifty years ago, although in 

 185 1 Scott Archer had shown to the world the practicability 

 of taking photographs on glass by means of collodion. In 

 that same year, when the First International Exhibition 

 was held, calotype, Daguerreotype, and collodion processes 

 were all worked commercially, and photographs of the 

 mterior of the Palace by all three processes are in being- 

 to-day. '' 



Af the present time it may be said that for all practical 

 purposes the gelatine process for taking negatives has com- 

 plete possession of the field, and ousted all processes which 

 have led up to it. Negatives fifty years ago were im- 

 pressions only given by the violet and blue rays existing 

 in white light, and the resulting prints are such as would 

 ■be seen by a person colour blind to the red and the green, 

 whilst now it is not uncommon for the photograph to be 

 made to coincide with visual impression of an ordinary eye 



I here seems but little doubt that the photographic image 

 remains of the same nature now as it was then, and what- 

 ever may have been the action of light then, so it is now 

 but the necessary exposure to obtain a properly developable 

 image was at least sixty-fold more than is required for our 

 present process, even when the collodion process was em- 

 ployed, where every condition remained the same except 

 the sensitive surfaces themselves. With the Daguerreotype 

 process perhaps we should have required ten times more 

 than for the collodion, though we know of instantaneous 

 work being done even with that process. For open air 

 portraiture, the early Daguerreotypist required half an hour 

 in bright sunshine, whilst the modern amateur will be 

 content with a second or a fraction of a second in the 

 same circumstances. A question one naturally asks is 

 What causes the difference? So far as I am aware this 

 question has not been fully answered, and yet it might 

 have been had serious experiment been undertaken regard- 

 ing it. ° 



From a theoretical standpoint there are three things that 

 have to be taken into account :— ist, the sensitiveness of 

 the silver salt itself; 2nd, the mediums in which it is 

 placed; and 3rd, the means of- development. We have 

 some clue to the last two. Beginning with the last first 

 those who practised Talbotype or the wet collodion pro- 

 cesses know that in both of them the developing solution 

 was an acid solution reduced from nitrate of silver which 



^^f.^Ln f^^"'/^f''^ °^ ^"^^ P^^*^ °'' P^P^""- *« ^he metallic 

 state, and that there was some attractive force which caused 

 tne metallic si ver to adhere to and crystallise on particles 

 of sensitive salt which had been acted upon by light In 

 the gelatine process we know that development is with 

 alKal.ne solution and that the image is built up from the 

 very molecules themselves that have been acted upon the 

 sensitive sa t itself being reduced to metallic silver. Why 

 should development be effected more easily in the one case 

 than in the other? In the case of the acid development the 

 distance of the particles of reduced silver from the mole- 

 cules altered by light are far greater than they are when 

 the material of the plate is attacked, and consequently 

 a smaller attractive force, due to fewer molecules beine 

 altered in the latter case, is efiRcacious in producing a silver 

 image than in the first case where the depositing silver has 

 a considerable distance into which the attractive force has 



JJO 1752, VOL. 68] 



to be exercised. This might be an explanation. Or, again, 

 it may be shown that a gelatine film, being a kind of filter 

 to the developing solution, acts as a regulator in allowing 

 the active alkaline solution to reach the particles of silver 

 salt, and that this regulated supply would attack the mole- 

 cules on which light had done part of the work of decom- 

 position, and reached the remaining part most readily to- 

 be finished and so on, and that very little external retarding 

 influence was necessary. But now, what is to be said re- 

 garding the increased instability of the sensitive salt? 

 This is a question not yet investigated, but it is from such 

 an investigation that increased rapidity is to be looked for. 



But it is one thing to say what proof is required, and it 

 is another to have the opportunity of making such proofs, 

 and I should urge that it is part of the duty and functions, 

 of the Royal Photographic Society to lead the way in 

 placing such means at the disposal of its members 'and 

 others as will enable any of them who have the capacity 

 to experiment in this and in any other directions which will 

 lead to a theoretical knowledge of the action of light. It 

 must not be forgotten that there are a great many more 

 men with minds trained to scientific research now than 

 formerly. There are plenty of would-be capable workers 

 who cannot afford a laboratory of their own, and what I 

 should wish to see in this our jubilee year is the commence- 

 ment of the formation of a research laboratory adapted to- 

 the needs of the scientific workers. 



One branch of photographic science is the optical, and in 

 it we have an example of what laboratory and experimental 

 research can do when workers are trained in scientific 

 methods. Not many years ago the optician was challenged 

 to increase rapidity of exposure by increased rapidity of 

 lens. Nobly and rapidly he has responded ; the advent of 

 Jena glass enabled him to comply with the demand, and we 

 have been getting definition of image with ratio of aperture 

 to focal length which would have been deemed impossible 

 not very many years ago. 



I do not believe a laboratory would be an expensive matter 

 to start. What I do advocate is to have all essentials of 

 all instruments of first-class workmanship, and to leave the 

 adaptation of any instrument from one special work to that 

 of another to the worker. Hence, if my views are carried 

 out, the initial expenses will not be so great as might be 

 supposed. Space is the foundation of all research in photo- 

 graphy, and that is what the Royal Photographic Society 

 can supply, and then comes the provision of the apparatus 

 necessary to use in such space. 



I have heard that one generous man will give looZ. to 

 the laboratory if gooZ. more are raised. The 1000/. would 

 go a very long way towards what we want to start with, and 

 I hope the members of the Society will resolve to give sub- 

 stantial help in raising this gooZ. The jubilee of the Society 

 should be marked by some important piece of work, and 

 no bigger one and more requisite is, to my mind, to be 

 found than starting such a help to the advancement of 

 photography. 



RADIO-ACTIVE GAS FROM TAP-WATER.' 

 ■yiT'HEN Cambridge tap-water is boiled the air given off is 

 ' *• mixed with a radio-active gas. The existence of 

 this gas is easily demonstrated by electrical means, for if 

 the air expelled by prolonged boiling from about 10 litres of 

 water is introduced into a closed vessel the volume of which 

 is about 600 c.c, the amount of ionisation in the vessel 

 (as measured by the saturation current) is increased five 

 or six times. When the water has once been well boiled 

 the gas expelled on any subsequent re-boiling is not appreci- 

 ably radio-active. The gas can also be extracted from 

 water at the temperature of the room by vigorously bubbling 

 air through it ; the air as it bubbles through the water gets 

 niixed^ with the radio-active gas and carries it along with 

 it. When water which has been treated in this way is 

 boiled, no radio-active gas is given out, nor is the gas 

 given off when air is bubbled through water which has 

 been well boiled. 



The gas extracted in this way from the water retains its 



i Paper read before the Cambridge Philosophical Society on May 4. 

 by Prof. Thomson, F.R.S. 



