578 



NA TURE 



[October i i, 1S94 



Sir John Herschel the first suggestion of spectrum photo- 

 graphy, and we find that in i S39 the latter pointed out that 

 the way to investigate sensitiveness was to photograph the 

 spectrum. In the following year he read a paper describ- 

 ing his results of spectrum photography. A little later, 

 in 1S4;, Becquerel and Draper were both at work photo- 

 graphing the solar spectrum. Twenty years later (in 

 1S64 Miller was turning to practical account the power 

 of photography to record the parts of the spectrum be- 

 yond the limits of human vision, and from that date 

 nearly all spectroscopic work has been photographic 

 work. Whether applied to astronomical observation or 

 chemical research, the spectroscope has always been 

 combined with the camera, and it is by the combination 

 of the two instruments that such wonderful results have 

 been attained. And as photographic methods have 

 improved, so have fresh facilities been afforded to the 

 spectroscopic worker. Mr. Lockyers earlier work was 

 of necessity done with wet plates, but with the plates 

 now available he is producing star spectra on a scale 

 comparable with the solar spectra of twenty-five years 

 ago.' Rutherford's recent maps of the solar spectrum 

 could not have been produced without the use of colour- 

 sensitive plates, while in one of the most recent attempts 

 to employ spectroscopic analysis for purposes of practical 

 metallurgy- Prof. Hartley tells us that he also used ortho- 

 chromatic plates, specially prepared, and that after try- 

 ing various developers he found hydroquinone the best. 



" As an automatic recorder of scientific observations, 

 photography seems to have been utilised in the Royal 

 Observatory about 1S47, under the superintendence of 

 the venerable ex-president of this Society, Mr. Glaisher, 

 who has been kind enough to furnish me with particulars 

 of the methods originally devised by Mr. Charles Brooke, 

 and successfully worked for many years by Mr. Glaisher 

 and his statT. 



"The method was first applied to record magnetic 

 variations and the movements of the barometer and 

 thermometer. In the case of the former, a ray of light 

 reflected from a mirror carried by the magnet was 

 focussed on the surface of a cylinder covered with sensi- 

 tised paper.'' The cylinder was rotated by clockwork, 

 the result being, of course — in the way now commonly 

 employed for such automatic records — to give, when the 

 image was developed, a record of the riovements of the 

 magnet. A base line was given by an invariable spot of 

 light, and by intermissions of this light a time record was 

 provided. Similar results were obtained in the case of 

 the barometer by using a float with a small perforation 

 through which the light passed, and with the thermometer 

 by simply allowing the mercury itself to screen the light 

 from the sensitive surface.' 



" Later on, in 1865, similar means were used by Mr, 

 Glaisher for the automatic record of earth-currents, and 

 they have consequently been continuously observed since 

 that date at Greenwich. 



"To the best of my knowledge but little alteration has 

 been made in the original system, the only improvement 

 being in the sensitive surface employed. When gelatino- 

 bromide paper was introduced, it was tried and adopted 

 at Greenwich, and by its means superior results were 

 obtained. 



" I have ventured to dwell at some little length on this 

 part of the subject, not because what I have said can be 

 novel to any of you, but because I think this first appli- 

 ration of photography to automatic observation has 



' lie of the Ilrighter Sun." /'Ai/. Tram., 

 ■ tnp«ralurel." PfiH. Tram , vol. 185, A., 



' fl employed was a rvrm of ihe old cnlotype process. Paper 



; -t.T-: n ^;r-n:-f'- nT'\ i'^li!- v-n-. nft.;rward» senftllited with 



vol. 



)>c m.nde 10 an adden- 

 .•I aod meteorological 



NO 1302. VOL. 50] 



considerable historical interest, and also because this 

 application was carried out by one so long and so 

 honourably connected with this Society. 



"The principle thus first applied at Greenwich has. 

 received numerous other applications, and indeed it is 

 now a matter of course that photographic methods 

 should be used to register the movements of any instru- 

 ment of whose indications it is desired to preserve a 

 record. Instances are of course numerous in which no 

 other method is possible. Hardly any but a photographic 

 method could register the movements of the light spot 

 of a reflecting galvanometer, and thusenable the physicist 

 who, like Langley, is measuring the heat radiated from 

 celestial bodies, to record the minutest dift'erences of 

 temperature ; the chemist, like Dewar, who is producing 

 hardly imaginable cold, to record temperatures approach- 

 ing absolute zero ; the metallurgist, like Roberts-.-\usten, 

 who is dealing with the melting points of metals, to 

 register by a photographically traced curve variations in 

 high temperatures which but a short time ago could not 

 be accurately measured at all. It is interesting to read 

 the testimony of the last named, given at the recent confer- 

 ence of the Camera Club, to the effect that he could not 

 conceive of any method which would give such results 

 in the same space and time. Equally interesting is it to 

 note the Professor's suggestion for a practical method of 

 recording continuously the temperature of the air-supply 

 of a blast furnace, a matter of great importance to the 

 iron manufacturer, of which he says : — ' If we had no 

 photography it would be impossible to get a record which 

 would be anything like so true.' 



" Numerous other instances will occur to many of you 

 in which photography has been or might be — indeed I 

 may say will be — applied to similar purposes. I will 

 only refer to one, because it appears to me so excellent 

 an instance of the delicacy of the method. At the 

 last (the Oxford) meeting of the British Association, Mr. 

 Burch showed to the newly-formed Physiological Section 

 photographic records taken with the aid of the capillary 

 electrometer of electrical currents produced by speaking 

 into the telephone. The letter z produced a complicated 

 curve in which oscillations of current lasting only i 3000 

 sec. were visible with a lens. 



"It seems hardly worth while to trouble you with 

 the detads of many of the other services which photo- 

 graphy has rendered to science, and if I were to attempt 

 to produce an exhaustive list, there are many present 

 tonight who could supplement it out of their own know- 

 ledge. The meteorologist has been enabled by its aid 

 to study the form and nature of clouds, the shape and 

 character of the lightning flash. The zoologist has been 

 taught much about animal motion. The microscopist 

 has long learnt to rely on the camera as the only 

 accurate means of reproducing the objects of his studies. 

 The physicist has by photographic methods investigated 

 many phenomena in which the changes are too rapid for 

 the human eye to follow them. By such means Lord 

 Rayleigh and Prof. Boys have obtained long series of 

 pictures of occurrences which all took place within a 

 fraction of a second, thus almost analysing time as the 

 chemist analyses matter. 



" The uses of photography in ethnology, geology, geo- 

 graphy, natural history, archa.'ology, arc too obvious to 

 need mention. They and many other applications may 

 be summed up in the remark that whenever the observer 

 of natural phenomena requires to make an accurate 

 record of his observations, photography supplies the 

 means. It also supplies the means of showing to a room 

 full of spectators what could otherwise be seen by but a 

 single observer at one time, and has thus rendered to the 

 popularisation of science no less a service than it has lent 

 to its advancement. This universal use of photography 

 for purposes of demonstration must certainly not be for- 

 gotten in however brief a suminary of its applications. ' .. 



