150 Geological Society. 



and — unfortunately for the first year student ! — the subject is too 

 large to be dealt with in a single volume. The text has been 

 largely re-written, and the author tells us in his preface that 

 three-fourths of the illustrations in the present volume are new. 



As the treatise is intended for students of electrical engineering, 

 everything which has no immediate practical bearing is excluded ; 

 this may account for the somewhat meagre treatment of electro- 

 statics, unless perhaps the author intends to return to it when 

 writing of capacity in the second volume. In explaining the laws 

 of conduction, hydrodynamic analogies, some of them very in- 

 genious, have been freely used, the student being properly 

 cautioned against pushing them too far. A description of the 

 various primary batteries is followed by an interesting calculation 

 concerning the relative cost of electric energy, when supplied by 

 primary batteries or by steam-engine and dynamo. After giving 

 the batteries every advantage, by neglecting their resistance and 

 local action and selling their waste products, the cheapest of them 

 (Daniell's) costs elevenpence per Board of Trade unit, while a 

 London generating station is able fo produce more than six units 

 for the same expenditure. In an appendix to the volume Professor 

 Ayrton gives a short history of the absolute unit of resistance and 

 of the Board of Trade electrical standards. 



The book has been thoroughly revised, and appears likely to 

 meet with a success equal to that of the first edition. J. L. H. 



XXIV. Proceedings of Learned Societies, 



GEOLOGICAL SOCIETY. 



[Continued from p. 75.] 



November 18th, 1896.— Dr. Henry Hicks, F.R.S., President, 

 in the Chair. 



HPHE following communications were read : — 



-*- 1. ' On Cycadeoidea gigantea, a new Cycadean Stem from the 



Isle of Portland.' By A. C. Seward, Esq., M.A., E.G.S. 



2. ' The Fauna of the Keisley Limestone. — Part II. Conclusion.' 

 By E. R. C. Reed, Esq., M.A., E.G.S. 



December 2nd. — Dr. Henry Hicks, E.R.S., President, 

 in the Chair. 



The following communications were read : — 

 1 . ' Another possible Cause of the Glacial Epoch.' By Prof. 

 Edward Hull, LL.D., E.R.S., E.G.S. 



In the introductory portion of the paper the author gives an 



