Notices respecting New Books. 163 



is complete. J. J. Thomson * has suggested that the re- 

 grouping of the constituents of the atom may give rise to 

 electrical effects such as are produced in the ionization of a 

 gas. Rontgen's j and Wiedemann's J results seem to show 

 that in the process of ionization a radiation is emitted which 

 has similar properties to easily absorbed Rontgen radiation. 

 The energy spent in producing uranium radiation is probably 

 extremely small, so that the radiation could continue for long 

 intervals of time without much diminution of internal energy 

 of the uranium. The effect of the temperature of the uranium 

 on the amount of radiation given out has been tried. An 

 arrangement similar to that described in § 11 was employed. 

 The radiation was completely absorbed in the gas. The 

 vessel was heated up to about 200° C; but not much differ- 

 ence in the rate of discharge was observed. The results of 

 such experiments are very difficult to interpret, as the variation 

 of ionization with temperature is not known. 



1 have been unable to observe the presence of any secondary 

 radiation produced when uranium radiation falls on a metal. 

 Such a radiation is probably produced, but its effects are too 

 small for measurement. 



In conclusion, I desire to express my best thanks to 

 Prof. J . J. Thomson for his kindlv interest and encouragement 

 during the course of this investigation. 



Cavendish Laboratory, Sept. 1st, 1898. 



IX. Notices respecting New Books. 

 A Treatise on Dynamics of a Particle ; ivitli numerous examples. By 



Dr. E. J. Eouth, F.R.S. Cambridge : University Press. 



Pp. xii -f 417. 

 npHAT this work is a thorough one on its subject is a matter of 

 -*- course, but it is more than this, it is a most interesting one. As 

 Dr. South remarks in the opening words of his preface, " so many 

 questions which necessarily excite our interest and curiosity are 

 discussed in the dynamics of a particle that this subject has always 

 been a favourite one with students." He puts the question, how- 

 is it that by observing the motion of a pendulum we can tell the 

 time of rotation of the earth, or, knowing this, can deduce the 

 latitude of the place ? Other such problems excite our curiosity 

 at the very beginning of the subject. When we study the replies 

 to those problems we find new objects of interest, and so we 

 mount higher and higher until we include the planetary per- 

 turbations, and take account of the finite size of bodies. So far 

 does Dr. Eouth carry us until he approximates quite closely to 

 his familiar Rigid Dynamics. One has hitherto associated his 

 work and name primarily with this latter subject, but as for 

 iome forty years the whole mathematical curriculum must have 

 jccupied his thoughts, he must have many potential books in his 



* Proc. Camb. Phil. Soc. vol. ix. pt. viii. p. 397 (1898). 



t Wied. Ann. lxiv. (1898). \ Zeit.f. Electrochemie, ii. p. 159 (1895). 



