Chemistry and Physics. 441 



advances in the science have been incorporated, many minor 

 improvements have been made, and numerous new references to 

 literature increase the value of the book for reference. 



H. L. W. 



7. Canal Rays. — A number of papers on this subject have 

 recently appeared : and the conviction appears to be gaining 

 that in these rays one has the best means of ascertaining the 

 nature of the positive atom. F. Paschen (Ann. der Physik, 

 No. 7, pp. 247-260) gives some remarkable photographs of the 

 Doppler effect m the canal rays produced in hydrogen. In the 

 main he substantiates Stark's investigation, but he differs from 

 him in regard to the distribution in the light of the displaced 

 lines or bands, in certain series of lines. In a second paper (pp. 

 261-206) Paschen gives an investigation of the Doppler effect in 

 oxygen. He employed a concave grating of 10 cm diameter and 

 3-03 meters radius. The papers contain interesting reflections upon 

 the relation of series lines and the Doppler effect. Stark (Ann. 

 der Physik, No. 9, pp. 798-804) answers the objections of Paschen, 

 and maintains that the latter's assertion that the series lines of 

 oxygen do not show the Doppler effect is not correct. Paschen 

 maintains his position in Ann. der Physik, No. 10, pp. 997- 

 1000. The most suggestive paper on the subject of canal rays 

 is one by J. J. Thomson (Phil. Mag., May, 1907, pp. 561-575). 

 The vacuum tube employed by Thomson Avas terminated at the 

 end of the tube in which the canal rays were formed, by a screen 

 covered with powdered willemite. The canal rays falling on 

 this screen produced a fleck of light and the deflection of this 

 spot of light by electric and magnetic fields was studied in vari- 

 ous gases. A variety of rays were discovered : for one kind 



£ 



- has the value of 10 4 , that of an atom of hydrogen : for another 



kind ■ - has half this value. A paper in Phil. Mag., Sept., 1907, 



p. 359-364) also by J. J. Thomson, shows that particles of posi- 

 tive electricity are shot off in all directions from the gas trav- 

 ersed by the canal rays. j. t. 



8. Propagation of Plane Electromagnetic Waves over Plane 

 Surfaces and their relation to Wireless Telegraphy. — J. Zennkck 

 gives a mathematical discussion of this subject, and its bearing 

 upon the absorption of such waves by the atmosphere. Marconi 

 has shown that the distance one can reach by wireless telegraphy 

 is 2^ times greater by night than by day and he attributes this 

 phenomenon to the increased absorption of the waves due to 

 ionization of the air by daylight. Zenneck's calculation shows 

 that the layers of air less than 6,000 meters from the earth's sur- 

 face cannot change their conductivity by daylight sufficiently to 

 account for the absorption of the waves, and he believes that this 

 absorption is due to the loss of energy from the antennae due to 

 daylight. It is probable also that the good effect of clouds and 

 fog is due to the protection of the antennae from this loss of 



