Photographing Ultra-Violet Spectra, ~ 97 



Although the form of apparatus employed by me has been 

 shown to those especially interested in the subject, yet no detailed 

 description has ever been published, partly by reason of the fact 

 that until the summer of 1879 only a temporary arrangement 

 was made use of, and it was considered probable that further 

 improvements might be effected. Constant use, however, has 

 shown that practically it leaves nothing to be desired. 



As an introduction to the publication of a series of photographs 

 of metallic and other spectra the description of the apparatus is 

 most appropriate. 



The instruments employed are the following : — First, an induc- 

 tion coil guaranteed to give a five to six inch spark in air, con- 

 nected with a Leyden jar, for the production of an unbroken 

 stream of dense sparks between metallic electrodes. Second, a 

 collimator tube ranging from fifteen to thirty-six inches in length 

 at the end of which is a quartz lens. Third, a quartz prism 

 capable of being placed at the minimum angle of deviation for any 

 particular ray. Fourth, another quartz lens and the body of a 

 photographic camera capable of being extended to the full focal 

 length of the lens. The separate portions of the apparatus parti- 

 cularly if lenses of thirty-six inches focus be used, should be firmly 

 fixed by means of screws to prevent the shifting of any part, since 

 the proper adjustment of the whole takes some time. The coil 

 is excited by a battery of five Grove's cells. The Leyden jar is 

 of such a size that each surface of tinfoil measures seventy-two 

 square inches. So far the general arrangement is that used by 

 Miller and others, the most important difference lies in the details 

 of construction of the camera. 



Description of the Photographic Camera. — Two cameras 

 have been in use — one designed for photographing with one quartz 

 prism and lenses of thirty-six inches focal length (vide Plates 12- 

 1 5), the smaller one adjustible for lenses of nine to seventeen inches 

 focus to which prisms of various refractive and dispersive powers 

 can be adjusted and with which two or more prisms can be used 

 by an alteration in the prism-table. This latter instrument 

 differs from the former chiefly in details allowing of very accurate 

 adjustments, and of great adaptability in the collimator-tube, the 

 prism table and the camera-body so that the requirements of the 



