Intelligence and Miscellaneous Articles. 655 



the student is told to watch several balls of the same size but of 

 different material rolling on the ground, will certainly not give a 

 vivid conception of the notion of mass. ' Heavy ' weights that 

 roll across a theatre stage often consist of the lightest materials, 

 but give the false impression intended. A student should himself 

 start or stop the balls in order to realize the difference between them. 

 Again, to prove that the elasticity of indiarubber is different from 

 that of glass by letting two balls of these materials fall on an oiled 

 glass plate and comparing the patches, is to make use of an experi- 

 ment far too recondite for the purpose. Why not merely stretch 

 two rods with equal weights ? The part dealing with elasticity is 

 scarcely satisfactory even allowing for the omissions necessary in 

 an elementary book. 



The rest of the volume (Heat, Electricity, Magnetism, Light) is 

 more to be commended, especially the Electricity. In connexion 

 with electric oscillations we may mention that it was Savary, not 

 Joseph Henry, who first magnetized needles in alternating layers 

 by the discharge of a jar ; and that Kelvin's prediction should be 

 dated 1853 not 1855. Bernoulli's name is spelled wrongly. 



Though the book does not attain to our ideal of what an 

 elementary one should be, there is so much about it to be praised 

 that we have no doubt that many will find it just the one they 

 want. 



LIX. Intelligence and Miscellaneous Articles. 



NEW GEOLOGICAL VIEWS OX TERRESTRIAL 31AGNETISM AND 

 VOLCANISM. BY J. J. TAUDIN CHABOT. 



r PHE development of heat by the disintegration of atoms needed 

 -*- only to be discovered to raise at once the question whether 

 the thermal phenomena of our planet are of the same kind, even 

 as previously the ascertained magnetic properties of some sub- 

 stances raised the question whether the magnetic state of the globe 

 arises from its being constructed of such materials. 



With regard to the first question, observed data tend to support 

 the possibility of its truth ; concerning the second we have reached, 

 so far, no satisfactory conclusion. 



The results of recent investigations appear, however, to open 

 up paths along which our knowledge may be extended, the most 

 remarkable of which is one that gives rise to the unexpected 

 idea of a possible connexion between the fundamental causes of 

 the thermal and magnetic phenomena of our planet. 



The spontaneous radioactivity (so-called) exhibits a definite 

 dependence upon atomic weights inasmuch as it has been detected 

 in those substances whose atomic weights have the highest 

 known values. Thus it was discovered in a uranite, and imme- 

 diately afterwards it was observed iu thorium ; whilst the more 

 recently found radium has also a high (perhaps even the highest 

 known) atomic weight. This last substance follows bismuth in a 

 direct series leading up from radioactive lead ; and of bismuth we 



