Geological Society. 363 



mathematical knowledge required, really only adapted for quite 

 advanced classes. The explanation of the rectilinear propagation 

 and of the reflexion and refraction of light as a consequence of the 

 undulatory theory is remarkably clear ; and the difficult subjects of 

 diffraction and double refraction are well put. A discussion of 

 Fresnel's and McCullagh's theories of polarized light is given : the 

 discussion is difficult, and the results doubtful and discrepant, so 

 that it seems rather beyond the scope of a " Text-book." The first 

 chapter treats of the wave-motion of light as a form of energy ; and 

 the fifteenth chapter discusses the probable relations of light, 

 electricity, and magnetism as vibrations of the same material ether : 

 these chapters are most important in a theoretical view. 



The work is well got up, and contains few misprints for the 

 amount of matter. The expression "wave-surface centre A" 

 occurs frequently as short for " wave-surface whose centre is A ; " 

 a preliminary explanation would have been useful. The innovation 

 in fractional notation sin </>/sin (f>' is occasionally used (without 

 explanation) ; having been thus to some extent adopted, it might 

 have been used much more frequently with considerable gain in 

 conciseness. Allan Cunningham, Major R.E. 



Transit Tables for 1883 for Popular Use. By Latimek Clabk, 

 M.I.C.E. (London, A. J. Frost, 1883 : pp. 15 + 103 of Tables.) 

 These may be looked on as a sort of small Nautical Almanac 

 for amateurs for taking time with a small transit, and are suffi- 

 cient for the purpose when taken in conjunction with the same 

 author's ' Treatise on the Transit Instrument &c. for the use of 

 Country Gentlemen,' reviewed in No. 88 of this Magazine. As an 

 aid to popularizing the use of the portable transit their publication 

 may be welcomed. Allan Cunningham, Major R.E. 



JJIII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 298.] 



March 7, 1883.— J. W. Hulke, Esq., F.R.S., President, 

 in the Chair. 

 rPHE following communications were read : — 

 J- 1. "On Gray and Milne's Seismographic Apparatus." By Thomas 

 Gray, Esq., B.Sc, F.R.S.E. Communicated by the President. 



This apparatus was stated to have for its object the registration of 

 the time of occurrence, the duration, and the nature, magnitude, and 

 period of the motions of the earth during an earthquake. The in- 

 strument was made by Mr. James White, Glasgow, and is to be 

 used by Prof. John Milne in his investigations in Japan. 



In this apparatus two mutually rectangular components of the 

 horizontal motion of the earth are recorded on a sheet of smoked 

 paper wound round a drum, kept continuously in motion by clock- 



