Notices respecting New Books. 301 



the sphere the simple expression 



sin r , 

 v= — — e~ K . 

 r 



Substituting this in (3) we find that dK/dt vanishes when 



, Sr 



tan r— ^ 5. 



o — r* 



This equation for the level of no strain is satisfied by ?» = 0, 

 the next positive root lies between §7r <md 2ir, the following- 

 one between |7r and 3^ and so on. All except the first lie 

 beyond the limits of the radius of the sphere. 



Now from to it tanr is greater than 3r/(3— r 2 ), and 

 dv/dt is greater than Srcdv/rdr. 



Hence the level of no strain is constant in position and is 

 reduced to a point at the centre of the sphere. All the 

 strata are compressed. 



The assumed law of temperature gives a very great gradient 

 in the upper strata, so that it is not applicable to the case of 

 the earth. But it shows that generally (and it is obvious 

 itself) the level of no strain lies deeper, when the initial tem- 

 perature increases from the surface to the centre. 



I wish to draw the attention of geologists and geophysicists 

 to this, as a consideration to be taken into account in deducing 

 conclusions on the contraction of the earth as a cause of 

 mountain-building. 



XXXII. Notices respecting New Books. 



The Principles of Chemistry. By D. Meistdeleeff. Translated 

 from the Russian by George Ka.men"SKT ; edited by A. J. 

 Greewaway, F.I.G. Two Vols. Longmans, Green, & Co., 1891. 

 T^NGLISH chemists have had long to wait for the appearance of 

 •*-* this work in their own language, but the delay is excusable 

 when we consider the difficulty of faithfully rendering the ideas of 

 the illustrious Eussian author, expressed originally in a tongue 

 which is strange to almost every chemist in this country. Both 

 translator and editor have, however, performed their respective tasks 

 in a highly creditable manner, and although lingering traces of 

 ambiguity here and there reveal the difficulties with which they 

 have had to contend, the book as a whole reads with remarkable 

 smoothness. It would be impossible within the compass of this 

 notice to give any adequate notion of the contents of the two 

 volumes comprising Mendeleeff's work. It is both a natural 

 history of the chemical elements and their compounds, and a 

 philosophical treatise setting forth the general laws and principles 

 which underlie chemical transformations. Not the least impor- 

 tant among its claims to rank as one of the classics of chemical 

 Phil. Mag. S. 5. Vol. 34 No. 208. Sept 1892. Y 



