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A LABORATOEY FOR PHOTOGRAPHIC RESEARCH. 



BY ROMYN HITCHCOCK. 



The discussion upon the respective merits of ordinary and 

 color-sensitive plates for photographing stars, which has been 

 raised by the French astronomei-s, is only a single example out of a 

 great number which might be mentioned to show bosv much ex- 

 perimental work has yet to be done before our photographic pro- 

 cesses will fully meet the demands of scientific investigation. 

 Modern photography has experienced very rapid development. 

 It has been such a fascinating subject for experimentation that a 

 great host of workers, many of them skilful and indefatigable, 

 have contributed a countless array of facts, but intermingled 

 with these are so many observations of a different character that 

 the extensive literature of the subject is very confusing. What, 

 for instance, are we to understand concerning the remarkable 

 phenomena observed by several of the early investigators who 

 found that certain rays of the spectrum produced chemical 

 changes which were reversed by certain other rays? It has 

 seemed to me that this subject would well repay investigation 

 with the improved appliances and better knovidedge of the present 

 time. The latest application of the phenomenon that has come 

 to my notice has been at the astro physical observatory at Wash- 

 ington, in an attempt to photograph the invisible infra-red spec- 

 trum by means of a phosphorescent plate. The rays of the spec- 

 trum destroy the phosphorescence, leaving luminous bands repre- 

 senting the spectrum lines. It is not probable that any such 

 method will prove of much practical value, but none the less is 

 the investigation of the phenomenon to be advocated for the in- 

 formation to which it may lead concerning the nature of radiant 

 energy. 



The fact that Professor Langley has resorted to such a device to 

 photograph the invisible part of the spectrum brings clearly before 

 us the supposed limitations of photography in this direction. 

 The limits of the photographed spectrum have within a few years 

 been greatly extended into the red, and even beyond it perhaps, 

 by special sensitizing agents or by peculiar methods of preparing 

 plates. But the theory of the subject has not been worked out, 

 and in this there is a very important field for research. The in- 

 ducements to carry out such investigations must come from those 

 who most need the results. In other words, here as in other 

 cases the photographic investigator would like to know that his 

 results will be intelligently applied, else he becomes discouraged 

 and enters ui^on some other tiekl. If the pliysical observer 



would encourage research in photography to meet his require- 

 ments, and if the astronomer would have plates perfectly adapted 

 to his purpose, let them cease to place their reliance upon color- 

 sensitive plates, or on any other plates prepared for the public de- 

 mand, and put their photographic work in the hUnds of an expe- 

 rienced photographic chemist — not a mere operator picked up in 

 a gallery or among amateur experimenters — but one who can 

 apply the latest discoveries to the work in hand. It is because 

 investigators who are not trained photographers, familiar with the 

 processes and discoveries of the time, have undertaken to do the 

 most difficult kind of photographic work themselves, that the 

 results are so frequently inferior to what they might be. It is 

 certainly a fact that the best photographic knowledge we possess 

 is not generally applied to scientific work. 



It is upon such grounds as these that I have long advocated the 

 establishment of a photographic laboratory for research in con- 

 nection with one of our great iustitutions. Such a laboratory 

 would not only lead to important discoveries and improved 

 methods, but it would give an impetus to the study of photog- 

 raphy as a science involving chemistry and physics, in ijreparation 

 for work in various branches of science. The problems presented 

 in the observatory and in the spectroscopic laboratory could then 

 be systematically studied, as they cannot be by the workers in 

 these different fields. For example, the astronomer desires plates 

 for photographic star- maps, which shall be uniform in character 

 and rapidity, unaffected by temperature or moisture, free from 

 granularity and without the tendency to " halation " by long ex- 

 posures. More than this, an effort should be made to produce a 

 plate which will reproduce fairly well the relative actinic magni- 

 tudes, if I may coin the expression, if not the visible magnitudes 

 of stars. That such plates can be produced scarcely admits of a 

 doubt, but to establish the fact requires some, perhaps a great 

 deal of experimenting. But having once accomplished the re- 

 sult, it would be a boon to astronomy sufficient in itself to justify 

 tie existence and liberal endowment of such a laboratory. The 

 mere discovery of a means to produce plates of absolutely uniform 

 sensitiveness, measured in units of time and also spectrographi- 

 cally, would be of incalculable benefit to physical investigation. 

 As regards the granularity of the image, it has been clearly 

 demonstrated that this is greatly influenced by the development, 

 particularly with certain plates more than others. 



Now as regards plates for other special purposes, to men- 

 tion a case in point, I refer once more to Professor Langley's 

 desire to photograph the part of the spectrum which he has so 

 ingeniously mapped with the bolometer. No one has questioned 

 the accuracy of the indications of that instrument, but it would 

 certainly be of interest to see a. photographic reproduction of at 

 least a portion of that invisible spectrum, to compare it with the 

 bolometric curves. It would enable us to interpret the latter with 

 much more confidence when it becomes desirable to reduce the 

 curves to spectrum lines. 



As ah-eady stated, considei'able work has been done abroad in 

 extending the photographic action of the red rays of the spec- 

 trum. Schumann, for example, has photographed the spectrum, 

 showing line A distinctly and for some distance beyond. 



But when we consider the enormous extension of the invisible 

 spectrum beyond the blue, recently photographed by Jlr. Schu- 

 mann,- on plates especially prepared for the purpose, we have an 

 indication of the possibilities of scientific research in photogra- 

 phy. There is really no reason to suppose that we have reached 

 the photographic limit in the less refrangible eud of the spec- 

 trum. 



The interesting phenomenon of the sun's corona has led to many 

 attempts to photograph it on the rare occasions offered by total 

 solar eclipses. B.ut so little have the photographic conditions 

 been considered in this connection, that, as I have elsewhere re- 

 marked, the government photographic expe'lition was sent to 

 Japan without a photographer, and the expedition to Africa went 

 with commercial color-sensitized plates. Now, it would be inter- 

 esting to learn the reason for the selection of those particular 

 plates for the corona. While I am not prepared to say that they 



' Hitchcocfe, R. The latest advances in spectrum photography. Science^ 

 Feb. 36, 1892. 



