﻿X dices respecting New Boohs. 93 



is much greater than that of the a. particles from the other 

 products. 



Sole. — In the previous paper [ mentioned that some 

 experiments were in progress to settle definitely Whether the 

 activity of radiothorium decays appreciably with the time or 

 not. It was state;! that two standard watch-glasses showed a 

 decrease ot activity and that another sealed watch-glass was 

 under investigation. The activity of all these specimens 

 decays -lowly, though apparently not very regularly, and 

 sufficient time has nor yet elapsed to give the period oi: decay 

 with any certainty 



In addition, I wish to state that in the first paper on radio- 

 thorium in the Jalirbuch der Radioaktivitat unci Elektronik. 

 there occurred a misprint, giving the time for radio thorium 

 to be half transformed as 109 years. The number was meant 

 to be 10° years, and gives the period of thorium itself, not of 

 radiothorium. 



In conclusion it is with much pleasure that I express my 

 gratitude to Professor Rutherford for suggesting this work, 

 for his kind assistance, and for the interest which he took in 

 the experiments. 



McDonald Physics Building, 

 McGill University, Montreal, 

 May 15, 1906. 



XI Y. Notices respecting New Books. 



Die Fortschritte der Rinetisclien Gastheorie. Ten Dr. Gr. Jager, 

 Professor der Physik an der technischen Hochschule in Wien. 

 Mit 8 eingedruckten Abbildungen. Braunschweig : F. Yieweg 

 undSohn. 1906. Pp. xii+122. 



HTIIIS monograph, which forms No. 12 of the series now being 

 published under the general title of Die Wissenschaft. is one 

 of the clearest expositions which we have come across of the kinetic 

 theory of gases and its recent advances. It is just the sort of 

 account to satisfy the demands ot a physicist as distinguished from 

 a pure mathematician. The kinetic theory has recently assumed 

 fresh importance in view of the developments of the electronic 

 theory. The first half of the book under review contains a 

 delightfully lucid and remarkably simple account of the older 

 portions of the kinetic theory, while the remainder is concerned 

 with its more recent developments, and includes such subjects as 

 the temperature-coefficient of viscosity, discontinuity of tempe- 

 rature in heat conduction, the intrinsic pressure of fluids, the 

 viscosity of ideal fluids and the size of molecules. We can heartily 



