Geological Society. 785 



pponding to less refrangible monochromatic rays gradually 

 became more intense, and produced on the orthochromatic 

 plates a greater and greater effect ; while the contrary occurred 

 with the more refrangible lines. 



Having lately made a new spectrograph of the light 

 emitted by the above-mentioned lamp, I found that the group 

 of three lines, of the wave-lengths 3663*3, 3654*9, and 3650'3 

 Angstrom units, had nearly completely vanished; while the 

 three lines 5790*49, 5769*45, and 5460*97, which in the first 

 experiments had given a scarcely visible photographic im- 

 pression, now produced a much clearer and a more intense 

 impression than any other line ! 



The figure accompanying this note shows the comparison 

 of two spectrographs of the light emitted by the electric arc 

 in mercury vapour, the former of which was made when the 

 Uviol lamp was almost new ; the latter after the same lamp 

 (always fed by a continuous current of 60 volts and 2 to 

 3 amperes) had been working daring short periods separated 

 by long intervals, for about one hundred hours. 



As it is now generally believed that the vibration corre- 

 sponding to each line of the spectrum of an element must 

 be considered as due to its positive ions, I think the modi- 

 fication I have noticed in what Prof. Stark calls the first 

 linear spectrum of mercury, must be considered as depending 

 on an alteration in the character of the positive monovalent 

 ions, probably consisting in such a variation of the vibrating 

 mass, that it renders oscillations of a higher frequency im- 

 possible, while the vibrations of. less wave-length, due to a 

 state of a smaller capacity for motion, are made easier and 

 therefore intensified. 



We have still to find out whether this observation as to 

 probable material modification of mercury can be further 

 corroborated, and also whether it can even become permanent, 

 corresponding to a change in the internal constants of 

 mercury; and this 1 intend to be the subject for further 

 experimental researches. 



Padua, R. Istituto Teclmico, 

 October 5th, 1907. 



LXXVIII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 676.] 



June 19th, 1907.— Aubrey Strahan, M.A., F.R.S., Vice-President, 



in the Chair. 

 ^HE following communications were read : — 



1. ' The Inferior Oolite and Contiguous Deposits of the Bath- 

 Doulting District.' By Linsdall Richardson, E.G. 8. 



2. * The Inferior Oolite and Contiguous Deposits of the District 



