r 



Nov. 14, 1878] 



NATURE 



27 



bodies emit light with heat to be 977°, and shows ex- 

 perimentally that as the temperature of an incan- 

 descent body rises it emits rays of an increasing 

 refrangibility ; also that the amplitude of any parti- 

 cular vibration increases with the temperature, and 

 that to every particular wave-length there^belongs a parti- 

 cular colour. But even more remarkable are the deduc- 

 tions he makes regarding light and heat, deductions 

 which, though evident noii<, perhaps, in the present state 

 of knowledge, had by no means then the appearance of 

 undoubted truths. He boldly asserted that light and heat 

 were efifects of radiation and not forces existing in the 

 radiations themselves. 



It is, however, with photographic research that the 

 name of Draper is most generally linked ; and as his 

 researches in this line commenced in 1837, two years 

 before the announcement of Daguerre's and Fox 

 Talbot's discoveries, his claim to be considered one of 

 the pioneers in photography admits of no contravention. 

 In his memoir on " Studies in the Diffraction Spectrum" 

 we read : "Several years before the commencement of the 

 discovery of photography by Daguerre and Talbot (1839), 

 I had made use of the process for the purpose of ascer- 

 taining whether the so-called chemical rays exhibited 

 interference, and in 1837 published the results in the 

 Joiirfial of the Franklin Institute, Philadelphia (July, 

 1837, p. 45). In this, as will be seen by consulting that 

 publication, I was successful." In his memoir of 1843, 

 he describes the mode in which he photographed the spec- 

 trum, from the blue to the ultra-violet, and from near C in 

 the red region to a point some distance below the limit of 

 visibility. The apparatus he employed would at the 

 present time be considered, perhaps, somewhat rude, but, 

 as is well known, the roughest appliances in the hands of 

 a true philosopher are sufficient even for delicate expe- 

 riment. Thus, in photographing his spectrum we find that 

 he worked before the days of collimating lenses, and 

 with a consequent feebleness of light which was a 

 serious matter when the slow (as compared with that 

 now extant) process of Daguerre was employed for 

 registering the impressions of the radiations. Half an 

 hour's exposure was not too long to give to obtain a 

 developable image, whereas now as many seconds as he 

 gave minutes, with the same size of spectrum and width 

 of slit, would be more than ample. The method by 

 which Draper registered the hnes in the red and ultra-red 

 regions is fully treated of in his fifth memoir. The plate re- 

 ceived a preliminary exposure to white light, and was then 

 exposed to spectrum ; or feeble daylight was allowed access 

 to the plate whilst being similarly exposed; the result, on 

 development by mercury, being that the dark lines in these 

 regions were registered as light lines on a dark back- 

 ground, instead of as dark lines on a white background. 

 This action Draper, Claudet, and others ascribed to the 

 intagonism of the blue and red ray s which are found in white 

 light, and heads his memoir " Interference of radiations " 

 n consequence. Till last year this view of the antago- 

 pbism of rays was accepted as existent, when it received a 

 "blow, and probably a final one, from the announcement 

 of the experimental proof that this action was produced 

 |through the spectrum possessing the power of accelerating 

 the oxidation of the compound of silver which had been 

 :red by light, and which, when so changed became 



undevelopable. Whatever may be the explanation of 

 this phenomenon, we have in Draper's photographs of the 

 least refrangible region a gigantic feat, considering the 

 date at which it was performed. Though recent methods 

 may outstrip the more antiquated one as regards rapidity 

 of execution, yet it is due to him to acknowledge that 

 he has long priority in showing that chemical action 

 was not confined to the least refrangible end of the 

 spectrum. As regards the application of photography 

 to portraiture, to our author seems to belong the honour 

 of having taken the first portrait by the Daguerreotype 

 process, and the arrangements adopted for the purpose 

 read rather comically in these days of quasi-instantaneous 

 pictures. In his memoir, " C n Taking of Portraits by 

 Photography," he says : — " On a bright day, and with a 

 sensitive plate, portraits can be obtained in the course of 

 five or seven minutes in the diffused daylight. . . . Diffi- 

 cult parts of the dress . . . require intervals (exposure) 

 differing considerably, to be fairly copied, the white 

 parts of a costume passing on to solarisation before the 

 yellow or black parts have made any decisive representa- 

 tion. We have therefore to make use of temporary ex- 

 pedients. A person dressed in a black coat and open 

 waistcoat of the same colour must put on a temporary 

 front of a drab or flesh colour, or, by the time that his 

 face and the dark shadows of woollen clothing are evolved, 

 his shirt will be blue, or even black, with a white halo 

 around it." We are sure that the author cannot have 

 regretted the supercession of a process which entailed 

 such "dodging" to render a portrait practicable, more 

 particularly at the time when he sat for the photograph 

 from which the admirable portrait fonning the frontispiece 

 was engraved. 



To this same memoir we have also an append in which 

 it is shown that Dr. Draper had priority in taking a photo- 

 graph of the moon ; and when it is considered that the 

 exposure was twenty minutes, and the diameter of the 

 image about one inch, it would not be surprising had it 

 j lacked in detail. By an extract from the minutes of the 

 j New York Lyceum of Natural History we learn that in 

 j this photograph we have "a distinct representation of 

 j the moon's surface." 



To yet another discovery of Draper's we must refer, 

 since, like some others of his, it has been re-discovered 

 I quite recently. He says, in his description of the 

 Daguerreotype process, " On these principles" (he alludes 

 to the different photographic effects produced by different 

 rays of light) " it is plain that an achromatic object-glass is 

 by no means essential for the production of fine photo- 

 graphs ; for if the plate be withdrawn at a certain period 

 when the rays that have a maximum energy have just 

 completed their action, those that are more dispersed but 

 of slower effect will not have had time to leave any stain. 

 We work, in fact, with a temporary monochromatic 

 light." With a cigar-box as camera and a spectacle-lens 

 as an objective he tested his theory, and found that on 

 this principle he could photograph an engraving, with all 

 its finest details present. The similarity between Janssen's 

 use of an uncorrected lens for solar work and this is 

 apparent. 



Mixed up with photography is actinometry, and here 

 we find that Draper not only invented the chlor-hydrogen 

 photonieter, whic'i depends on the combinatirn of chlo- 



