February 



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i8] 



NATURE 



455 



elastic ether hypothesis which satisfied us in Maxwell's 

 days, we should carry on with no change in our 

 methods. 



Silvanus Thompson, in his inaugural presidential 

 address on the founding of our society, referred to the 

 youthfulness of that branch of engineering which we 

 practise. It recalled, he said, illuminations on the pro- 

 clamation of peace after the Crimean War. " Bengal 

 lights and rockets. How the vision of them stands out 

 in memory 1 But our society has as little to do with 

 fireworks as with fireflies. As little — and as much — 

 for, after all, both of them are assuredly of some 

 interest to the illuminating engineer." 



He knew that the secret of the firefly is still hidden 

 from us, but that if we knew it, -if we knew how to 

 produce the rapid vibrations which give the stimulus 

 called light, without producing all the slow ones as 

 well, as when we sound a high note with a finger 

 instead of pressing all the keyboard at once, the mechan- 

 ical equivalent of light would be as important as the 

 mechanical equivalent of heat, and we should be able 

 to produce light without heat. The quantity of energy 

 which apj>ears as useful light is about 2 per cent, of 

 the energy radiated from an electric glow-lamp ; in the 

 firefly it is about 96 or 97 per cent. In other words, if 

 we could produce a highly efficient lamp, the light- 

 generating output of a dynamo would be fifty times 

 greater than now, and 45 lb. of coal would do what a ton 

 does to-day. The cost of lighting will not be reduced in 

 anything like the same proportion. The cost of fuel 

 is about one-tenth of the selling price of the light. The^ 

 ordinarv London householder pays 3d. to di. for his 

 domestic lighting, which entailed a consumption of 

 about o-44d. of coal at pre-war prices. 



While so many engineers and scientific men have 

 been eager to do something for the war, and so few 

 have succeeded in finding any appreciation of their 

 services, our society must be content to have been 

 allowed to carry out more than one investigation for 

 which it was well fitted. Silvanus Thompson said that 

 fireworks, as well as fireflies, were of some interest to 

 the illuminating engineer. The star-shell, flares, and 

 parachute lights which play so important a part in the 

 war are but fireworks. The chemist has used his 

 skill to choose the most suitable compositions, and 

 ingenuity has been expended in putting them up and 

 in priming them ; but in estimating the results, no 

 further progress had been made beyond the stage of 

 Lambert— the eye alone was the judge. Fortunately 

 the right men in the right department were approached. 

 It was recognised that photometric tests would be use- 

 ful. Our society offered to find men who would sug- 

 gest methods and give their time, if necessary, to carry 

 out the work. A committee was accordingly formed; 

 it conferred with the experts, who cordially placed their 

 data and requirements before the members ; a special 

 photometer was at once discussed, designed, and made. 

 At the present time nothing more can be said than that 

 the instrument has fulfilled all expectations; it needs 

 no manipulation whatever during observations, 

 measurements may be taken over large ranges, and the 

 behaviour of unsteady or flickering lights can be re- 

 corded. The observations on a large number of sam- 

 ples, both of service patterns and of experimental kinds, 

 were made by the committee during night meetings, 

 and were reduced to candle-power-seconds per gram of 

 composition, and it is hoped that the resultV have been 

 useful. 



Some five and twenty years ago it seemed likely that 

 luminous paint would have many useful applications, 

 but the results were disappointing. The preparation of 

 one of the best kinds was kept secret, and it was never 

 properly placed on the market. Night operations of 



NO. 2519, VOL. 100] 



war have directed attention to this subject, and the old 

 method of exciting zinc sulphide or other materials by 

 light has given place to continuous stimulation by 

 o rays of radium compounds. Dials of watches and 

 compasses are well known, and luminous gun-sights 

 are no secret, but there are other applications which 

 cannot be described at present. On these a committee 

 of our members has been working. Tiny tubes are 

 used which are smaller and give less light than a glow- 

 worm, but in their preparation careful photometric 

 measurements of considerable difficulty have been made 

 and valuable information has resulted from the re- 

 search. 



More work is wanted, or at all events more accessible 

 literature is needed, on the physiology of vision. The 

 dioptrics of the eye are well understood; its normal, 

 abnormal, and pathological characteristics are the basis 

 of ophthalmic science. The theory of colour vision is 

 still, perhaps, unsettled, though no one worker will 

 admit it. The subject to which I wish to refer is a 

 purely quantitative one, and is the relation of light 

 flux to visual perception. The range of the luminous 

 stimulus to which the eye can respond is enormous. 

 When we grope our way on so dark a night that objects 

 are only just visible, the illumination is about one-ten- 

 thousandth of a foot-candle, or equal to that received 

 from a candle at a distance of 100 ft. In summer 

 sunshine we often have 5000 foot-candles, and in clearer 

 atmospheres than ours 10,000 foot-candles are reached. 

 The brightness of a furnace is even higher, and furnace- 

 men judge the temperature by the colour. 



By some marvellous organic control the eye so reacts 

 that it is capable of Estimating difference of tone and 

 colour over a range of several thousand millions. The 

 contraction of the pupil has very little to do with this 

 regulation. It merely seems to take advantage of a 

 greater stimulation to reduce spherical aberration. 

 Over a large part of the enormous range Fechner's 

 relation between stimulus difference and sensation 

 difference holds good. There must be some intricate 

 and delicate provision, perhaps, of a chemical chaiii;' 

 in the receptive portion of the eye, the retina, depend- 

 ing on saturation or exhaustion of material ; or some 

 inhibition of the transmissive portion, the optic nerve, 

 or some compensatory reaction or opposing activity 

 or fatigue in what Huxley called the sensificatory por- 

 tion, the brain. The automatic adjustment of control 

 which permits so sensitive an organ to accommodate 

 itself to such great changes in the external stirnulus 

 has its counterpart in other organs and functional 

 mechanisms of the body, such as those which are con- 

 cerned in, breathing. If physiologists could tell us 

 something about this quantitative control, it would 

 help us in several ways. 



SCIENCE AND THE COLD-STORAGE 

 INDUSTRY A 



THE value of perishable produce imported into this 

 country, subject more or less to refrigeration, 

 was, before the war, about 130,600,000?. per annum. '''^ 

 is abundantly evident that the most natural mean^ 

 preserving foodstuffs, v'z. by methods of low tempi ; 

 tures, have gained the confidence of our merchants, an 1 

 the cold-storage industry to-day is a striking example 

 of the successful combination of srienrr, commorro, 

 and industry. The history of th<> < ,.!.l--i(i! !-• iimvo- 

 ment reveals four outstanding featun - ; 



(i) It is difficult to imagine a more striking example 

 than the cold-storage industry affords of the success 

 of the spirit of enterprise and love of adventure which 

 have always characterised British commerce. 



1 From .1 paper read before tVie Royal Society of Arts on December 19, 

 1917, by Prof. J. Wemyss Anderson. 



