Geological Society. 313 



Scientia. La Theorie cle Maxwell et les Oscillations Hertziennes. 

 By H. Poincaee. Paris : Georges Carre et C. Naud, 1899. 



This volume represents the contribution of M. Poincare to the 

 series of records of scientific progress which are beiug issued under 

 the title " Scientia." British readers who are acquainted with 

 the modern development of the electromagnetic theory of light 

 may possibly suppose, from the nature of the author's previous 

 work on the subject, that the present volume is of a mathematical 

 character. This is, however, by no means the case, for the book 

 does not contain a single equation or formula ; when mathematical 

 analysis is referred to its results are stated in a manner which 

 caunot fail to be acceptable to the general reader. 



The work commences with an introductory chapter chiefly 

 devoted to the definition of terms ; this is followed by chapters 

 giving an explanation of Maxwell's theory, and an account of the 

 experiments of Peddersen together with Lord Kelvin's theory of 

 the oscillatory discharge of a condenser. The various forms of 

 apparatus used for exciting and for detecting Hertzian waves 

 are then described, after which the author proceeds to give 

 an account of researches on the propagation of the waves along 

 wires, in air and in dielectrics respectively, treating each in 

 historical order. A chapter is then introduced containing a 

 description of the more recent forms of exciter for obtaining and 

 detecting very short waves, and the volume closes with an account 

 of researches which establish the identity of optical and electro- 

 magnetic waves. All this is compressed into eighty small pages, 

 so that the treatment of each section is necessarily brief ; the 

 author's statements are, however, concise and to the point, and he 

 has faithfully carried out the intention of the editors to make the 

 series an expose of contemporary progress. J. L. H. 



XXXIV. Proceedings of Learned Societies. 

 GEOLOGICAL SOCIETY. 

 [Continued from p. 165.] 



April 26th (con*.).— W. Whitaker, B.A., F.R.S., President, 

 in the Chair. 



2. ' The Limestone-Knolls below Thorpe Pell, between Skipton 

 and Grassington in Craven.' By J. B. Dakyns, Esq., M.A. 



A band of limestone runs from Cracoe towards the north-east, 

 folded in an anticline and dipping under shales. In several places 

 the top of the limestone is brecciated and the overlying (Bowland) 

 shale contains fragments of limestone. The limestone forms five 

 abrupt conspicuous hills. The rocks in most of these hills are not 

 bedded, and where they are bedded the dip is confusing ; both in 

 exposures outside of these and in adits inside, the limestone in 



