Chemistry and Physios. 301 



the exact position which our sun, judged by spectroscopic evi- 

 dence, should occupy among its fellows. In his previous volume, 

 "The Meteoritic Hypothesis," he has brought forward the argu- 

 ments for believing that the primordial matter was not, as the 

 Nebular Theory assumes, an intensely heated glowing gas, but 

 was a meteoric swarm or a congeries of such swarms, which by con- 

 densation and consequently closer and more frequent impact, pro- 

 duced an increasing heat and continued to rise in temperature until 

 the loss became equal to the gain. Hence he says: "The idea which 

 one arrives at by a discussion of all the spectroscopic facts is that 

 we begin with a condition in which meteorites in swarms and 

 streams are very far apart, and from the collisions of these a spec- 

 trum results which gives us bright flutings and lines, in other words 

 the spectrum of the nebulae ; when they become a little more dense, 

 we get the bright line stars; and as they become denser still we 

 find the stars with a mixture of bright and dark flutings. Then 

 still more condensation and dark lines and at length the highest 

 temperature of all; after which begins a descent on the other side 

 till at last we end in cool dark bodies like the earth and moon." 

 Of his five groups, the author selects the Orion nebula as the 

 type of the first, a Herculis as the type of the second, a Cygni as 

 that of the third, Sirius as that of the fourth and Arcturus as that of 

 the fifth. The maximum temperature being reached in the fourth 

 group, those stars in previous groups are rising and those in suc- 

 ceeding groups are falling in temperature, our own sun belong- 

 ing to the fifth. While broadly speaking the hypothesis before 

 us is a real advance over its predecessor, yet as to matters of detail 

 it has not received, we believe, the general assent of astronomical 

 spectroscopists. Thus, for example, it is extremely difficult if not 

 in many cases impossible to distinguish a star of the third group 

 from one of the fifth ; i. e., a star which is supposed to be rising 

 in temperature from one which is falling. Still the book places 

 the arguments in a clear light and cannot fail to be of use in help- 

 ing us to reach a final conclusion. G. f. b. 



8. Nature of Rontgen Rays. — Professor G. G. Stokes states his 

 belief that these rays are transverse vibrations of the ether, and 

 that the cathode rays are streams of rapidly-moving particles. 

 He conceives of the apparent transparency of thin aluminum 

 plates to the cathode rays as the result of a process similar to 

 that which happens to a copper plate immersed in a sulphate of 

 copper solution which is undergoing electrolysis. On one side 

 copper is separated, on the other is dissolved. The deflection of 

 the cathode rays by magnetic and electrostatic force, Stokes 

 regards as a great objection to their being considered light rays. 

 According to his views the Rontgen rays are impulses, and not 

 vibrations. — Manchester Memoirs, 41, Part iv, 1896-97. J. t. 



9. Impulse theory of X-rays. — Following Professor Stokes, 

 Professor J. J. Thomson has elaborated the impulse theory of 

 X-rays from the point of view of the electro-magnetic theory of 

 light. When a rapidly- moving electrified particle is stopped, 



