94 



ScUntlflG F roceediiigs, Royal Bahlin Society. 



of many metallic elements were reproduced by mezzo-tint engraving 

 and can be seen in the Philosophical Transactions, Part I., 1863, 

 and also in the Journal of the Chemical Society, 1864. Having 

 compared the engravings with the original negatives and with 

 prints taken therefrom I can testify to their being faithful repre- 

 sentations, but the character of the metallic lines is wanting in 

 delicacy of detail and sharpness, such as we are accustomed to see 

 in the visible spectrum. The reason of tliis will be explained 

 further on. The photographic process was carried out with 

 films of plain iodized collodion and a nitrate of silver bath, 

 occasionally a bromo-iodized collodion was used, the developer 

 being pyrogallic acid. 



M. Mascart has examined the ultra-violet portion of the solar 

 spectrum by means of photography, and has given us a drawing 

 of a normal spectrum extending beyond H (Annales de I'Ecole 

 Normale, 1864). By the use of gratings engraved on glass by 

 ivl. Nobert, and prisms of Iceland spar, he has made measurements 

 of the wave-lengths of the ultra-violet solar rays as well as of the 

 lines of cadmium, the spectrum of this metal being remarkable for 

 the range beyond H, to which its rays extend. 



There is a regular diminution in wave-length from the solar 

 line H, \=396 to 221-7 the extreme line of cadmium. It is 

 i-emarkable that the shortest wave-length measured 221-7, 

 together with the longest visible undulation. A, X=7G0 consti- 

 tutes with the intermediate vibrations a scale extending nearly 

 two octaves. (Annales de I'Ecole Normale, 1867.) 



In the accompanying table the wave-length of the ultra-violet 

 lines of cadmium as measured by M. Mascart are given. Frequent 

 reference will be made to these measurements. 



Wave-length of lines in that part of the S2)ectrum of cadmiwn more 

 refrangible than the solar line B. 



Nijmbers of reference 

 to Cadmium lines. 



9 

 10 

 11 

 12 

 ]3 

 14 



Wave-length. 



398-56 

 360-75 

 346-45 

 340-30 

 328-75 



Numbers of reference 



