NATURAL PHILOSOPHY. 1-11 



PHOTOGRAPHS OF SPECTRAL LINES. 



At the last meeting of the British Association (1861), Prof. Miller 

 exhibited photographs of various spectra, and read a paper on the 

 subject. The apparatus by which the spectra may be photographed 

 consists of an ordinary camera obscura attached to the end of a long 

 wooden tube, which opens into a cylindrical box, within which is a 

 prism glass, or a hollow prism filled with bisulphide of carbon. If the 

 prism be so adjusted as to throw the solar rays, reflected from a helio- 

 stat, upon the screen of the camera, and the wires which transmit the 

 sparks from a KuhmkorfFer coil are placed in front of the uncovered 

 portion of the slit, the two spectra are simultaneously impressed. The 

 solar beam is easily intercepted at the proper time by means of a small 

 screen, and the electric spectrum is allowed to continue its action for 

 two or three, or six, minutes, as may be necessary. He did not find 

 that anything was gained in distinctness by interposing a lens of short 

 focus between the slit and the wire which supplied the sparks, with 

 the view of rendering the rays of the electric light parallel like those 

 of the sun, owing to the absorbent action of the glass weakening the 

 photographic effect ; and the flickering motion of the sparks being 

 magnified by the lens, rendered the lines less distinct than when the 

 lens was not used. Although with each of the metals, including 

 platinum, gold, silver, copper, zinc, aluminum, magnesium, iron, 

 when the spark was taken in air, he obtained decided photographs, 

 it appeared that in each case the impressed spectrum was very nearly 

 the same, proving that few of the lines produced were those which 

 were characteristic of the metal. The peculiar lines of the metal 

 seemed chiefly to be confined to the visible portion of the spectrum, 

 and these had little or no photographic power. This was singularly 

 exemplified by repeating the experiment upon the same metal in air, 

 and in a continuous current of pure hydrogen. Iron, for example, 

 gave, in hydrogen, a spectrum in which a bright orange and a strong 

 green band were visible, besides a few faint lines in the blue part of 

 the spectrum. Although the light produced by the action of the coil 

 was allowed to fall for ten minutes upon a sensitive collodion surface, 

 scarcely a trace of any action was procured ; whilst, in five minutes, 

 in the air, a powerful impression of numerous bands was obtained. 

 It was remarked by Mr. Talbot that in the spectra of colored flames 

 the nature of the acid did not influence the position of the bright lines 

 of the spectrum, which he found was dependent upon the metal em- 

 ployed, and this remark has been confirmed by all subsequent observ- 

 ers. But the case was very different in the absorptive bands produced 

 by the vapors of colored bodies ; there the nature of both constitu- 

 ents of the compound was essentially connected with the production 

 of absorptive bands. Chlorine, combined with hydrogen, gave no 

 bands by absorption in any moderate thickness. Chlorous acid and 

 peroxide of chlorine both produced the same set of bands, while hypo- 

 chlorous acid, although a strongly-colored vapor, and containing the 

 same elements, oxygen and chlorine, produced no absorptive bands. 

 Again, the brownish-red vapor of perchloride of iron produced no 

 absorptive bands ; but when converted into vapor in a flame, this 

 gave out bands independent of the form in which it occurred com- 



