Chemistry and Physics. 239 



a gas produce other ions, although the force acting on them is 

 small compared with the force necessary to produce the ordinary 

 vacuum discharge. (Nature, vol. lxii, Aug. 9, 1900.) In the 

 present paper, he gives a more complete account of his investiga- 

 tions, and he is led to the conclusion that there is a great differ- 

 ence between the positive and the negative ions at low pressure, 

 and that the negative ions are much smaller than molecules. 

 There is not much difference between the rate of diffusion of the 

 positive and negative ions. The slow rate of diffusion may be 

 due to the negative ions being carried in groups of molecules, 

 and the rates of diffusion of positive and negative ions would 

 depend upon the size of such groups. When the current passes 

 between two electrodes, one inside the other, the conductivity, 

 when the electromotive force is small, is unaltered by reversing 

 the current. When this force is large, the conductivity depends 

 greatly on the direction of the force. The current obtained from 

 the inner positive electrode may be five or ten times greater than 

 that obtained when the inner electrode is negative. The reason 

 appears to be due to collisions if we attribute the production of 

 new ions to the negative ions. In order that new ions should 

 be produced by collisions, it is necessary that negative ions 

 should pass through the gas near the inner electrode where the 

 force is large. When the inner electrode is positive, all the nega- 

 tive ions pass through this region, and a large conductivity is 

 obtained. When the inner electrode is negative, only a few of the 

 negative ions pass through the space where the force is large and 

 the conductivity is much reduced. The increase in conductivity 

 is due to the negative ions, and not to the positive ions. The 

 positive and negative ions therefore possess different physical 

 properties. — Phil. Mag., pp. 198-227, Feb., 1901. i. t. 



13. Pecueil de Donnees JVumeriques publie par la /Soeiete 

 Franpaise de Physique. Optique par H. Dufet. Troisieme 

 Fascicule, pp. 787-1313, with volume title page and contents. 

 Paris, 1900 (Gauthier- Villars). — This highly valuable compilation 

 of physical data (see this Journal, vii, 472) has now reached its 

 Third Part, which completes the volume on Optics. It contains 

 the following tables : Table XVII, Rotary Power of Crystalline 

 Bodies, including chiefly quartz and sodium chlorate; also other 

 crystallized substances. Table XVIII, Rotary Powers of Bodies, 

 liquid or dissolved ; also those of vapors. Table XIX, Interfer- 

 ence Colors, according to Newton, Wertheim, Quincke, and 

 Rollet. These tables are complete to the close of 1898. A Sup- 

 plement, pp. 1173-1305, brought down to the end of December, 

 1899, contains tables of wave-lengths ; of refractive indices for 

 gases, liquids, and various important solids, etc. The whole is 

 printed with great clearness and full references are given to the 

 original authors. 



14. One Thousand Problems in Physics ; by William H. Sny- 

 der and Irving O. Palmer. Pp. 142. Boston, 1900 : Giim & 

 Co. — This little volume contains well selected problems, especially 

 suited to the use of teachers of Physics in the secondary schools. 



Am. Jour. Sci.— Fourth Series, Vol. XI, No. 63.— March, 1901. 

 16 



