480 Scientific Intelligence. 



(Pogg. Ann. xcviii, p. 382, 1856). He concludes that the Hall 

 effect is due to the shifting of the equipotential lines or surfaces 

 due to the electric current in a strong magnetic field. — Ann. der 

 Physih unci Chemie, No. 10, 1893, p. 316. j. t. 



13. Hand- und HUfsbuch zar Atisfushrung Physiko-chem- 

 ischer Messu?igen, von W. Ostwald, 1893, Leipzig (W. Engel- 

 mann.) — In this handy little volume of three hundred pages Ost- 

 wald has condensed the results of his extended and very excep- 

 tional experience in the practical details of the conduction of 

 research in physical chemistry. The chapters treating glass 

 blowing, weighing and the determination of solubilities and of 

 molecular weights contain many valuable suggestions about these 

 ordinary manipulations of the laboratory. Those on the deter- 

 minations of temperatures, pressures, densities, surface tensions, 

 heat quantities and critical data, together with those on optical 

 and electrical measurements have very especial' interest for the 

 physical chemist, and they would be of great service in purely 

 physical work. The descriptions and explanations are all admir- 

 ably clear, the book is practically arranged and well printed, and 

 it is accompanied by various separately printed tables which 

 materially enhance its practical value. j. e. t. 



II. Geology and Mineralogy. 



1. The origin of Crystalline Sc/iists. — In an address before the 

 Geological Section of the British Association, Mr. J. J. H. Teall, 

 combatted strongly the common idea that crystalline schists 

 belong exclusively to the earliest periods of the earth's history. 

 He expressed himself as follows : 



"The crystalline schists certainly do not form a natural group. 

 Some are undoubtedly plutonic igneous rocks showing original 

 fluxion ; others are igneous rocks which have been deformed by 

 earth-stresses subsequent to consolidation ; others* again, are sedi- 

 mentary rocks metamorphosed by dynamic and thermal agencies, 

 and more or less injected with 'molten mineral matter'; and 

 lastly, some cannot be classified with certainty under any of these 

 heads. So much being granted, it is obvious that we must deal 

 with this petrographical complex by separating from it those 

 rocks about the origin of which there can be no reasonable doubt. 

 Until this separation has been effected, it is quite impossible to 

 discuss with profit the question as to whether any portions of the 

 primitive crust remain. In order to carry out this work it is 

 necessary to establish some criterion by which the rocks of igneous 

 may be separated from those of sedimentary origin. Such a cri- 

 terion may, I think, be found, at any rate in many cases, by com- 

 bining chemical with field evidence. If associated rocks possess 

 the composition of* grits, sandstones, shales, and limestones, and 

 contain also traces of stratification, it seems perfectly justifiable 

 to conclude that they must have been originally formed by pro- 

 cesses of denudation and deposition. That we have such rocks in 



