1879.] On the Absorption of the Ultra- Violet Rays. 233 



January 9, 1879. 



W. SPOTTISWOODE, MA., D.C.L., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read: — 



I. " Researches on the Absorption of the Ultra- Violet Rays of 

 the Spectrum by Organic Substances." By W. N. Hartley, 



F. Inst. Chem.,F.R.S.E., F.C.S., Demonstrator of Chemistry, 

 King's College, London, and A. K. Huntington, F.Inst. 

 Chem., A.R.Sc. Mines, F.C.S. Communicated by Professor 



G. G. Stokes, Sec.R.S. Received October 10, 1878. 



(Abstract.) 

 Parts I and II. 



One of the authors of this paper, Mr. Hartley, having studied the 

 researches of the late Dr. W, A. Miller " On the Photographic Trans- 

 parency of Various Bodies," &c. (" Phil. Trans.," 1863, 1), and of Pro- 

 fessor Stokes, "On the Long Spectrum of Electric Light" ("Phil. 

 Trans.," 1863, 1), determined to study the action of organic substances 

 on the ultra-violet spectrum. In 1872, the apparatus of Dr. Miller 

 was reconstructed, and some experiments were made which showed 

 that it was capable of some slight improvements. Some time was 

 spent in testing the value of the photographic method of experiment- 

 ing as compared with that adopted by Professor Stokes, and pre- 

 ference was eventually given to the former, or rather to a combina- 

 tion of both methods, since occasional use was made of a focussing 

 screen either of uranium glass or of white paper steeped in aesculine 

 solution and dried. It was soon apparent that a wide field of 

 investigation was opened, and, with the assistance of Mr. Hunt- 

 ington, a systematic course of examination of organic compounds 

 was commenced at the beginning of the present year. In January, 

 1878, M. Soret published his " Recherches sur 1' Absorption des 

 Rayons Ultra- Violet par diverses substances" ("Archives des 

 Sciences Physiques et Naturelies, Geneve"), which includes the ex- 

 amination of many inorganic and some organic compounds. Though 

 this is a work of very great interest, it does not touch upon the sub- 

 ject of the present investigation, namely, the connexion between 

 chemical constitution and diactinic quality. M. Soret uses a spectro- 



YOL. xxviii. s 



