July 20, 1900.] 



SCIENCE. 



99 



It appears, therefore, that the same rap- 

 idly moving corpuscles which form the 

 kathode raj'S, and which give practically 

 the only concrete explanation of the Zee- 

 man effect, also form one constituent at 

 least of the Becquerel rays. In the latter 

 case it would appear that the escape of the 

 corpuscles is a result of violent internal 

 disturbances among the molecules of the 

 active substance. Such disturbances may 

 accompany a gradual change from an un- 

 stable molecular grouping to one that is 

 more permanent. This view removes all 

 difficulty concerning the source of energy 

 of these rays, a question which a few years 

 since caused a great deal of needless an- 

 noyance. 



The Becquerel rays developed by a given 

 active substance usually consist of a mix- 

 ture of rays, differing widely in their vari- 

 ous properties. Not all of these rays are 

 deflected by a magnet. In some instances 

 the rays are more similar to the X-rays 

 than to kathode rays, both as regards their 

 behavior in a magnetic field and their other 

 properties. In such cases it seems to me 

 probable that X-rays are in reality present. 

 Some of the magnetically deflectable rays, 

 which are nothing more than kathode rays, 

 naturally fall upon the active substance 

 itself. There is no reason why this bom- 

 bardment should not result in the develop- 

 ment of X-raj'S, just as it would in the in- 

 terior of a vacuum tube. That Lenard's 

 kathode rays are able to produce X-rays 

 even in the open air has already been shown 

 by Des Coudres.* 



The hypothesis of electrified corpuscles 

 has been employed, in a form which does 

 not necessarily imply the extreme small- 

 ness of the particles considered, by numer- 

 ous physicists. For example, Lorentzf 



* Wied. Ann., 62, p. 134, 1897. 



t Versuch einerTheorie der elektrischen und opti- 

 Bohen ErBoheinuDgen in bewegten Korpern. Leiden, 

 1895. 



found it useful in discussing the electrical 

 and optical phenomena in moving bodies : 

 while Helmholtz* has used it in his electro- 

 magnetic theory of dispersion. An expla- 

 nation of metallic conduction analogous to 

 that of electrolytic conduction has often 

 been sought. Recently this subject has 

 been developed quite extensively by Rieckef 

 whose results appear extremely promising. 

 The assumption of positive and negative 

 ions, difierent perhaps from those of ordi- 

 nary electrolysis, permits a very concrete 

 qualitative explanation of a great number 

 of well-known phenomena. Among these 

 may be mentioned the various thermoelec- 

 tric phenomena, the Hall effect, together 

 with its thermal analogue, and the Thom- 

 son effect. Views similar to those developed 

 by Eiecke have recently been supported by 

 J. J. Thomson. :|: 



Enough has been said to show that the 

 hypothesis of electrified corpuscles has 

 much in its favor. That the present form 

 of the hypothesis is very incomplete and 

 leaves much to be explained, no one would 

 attempt to deny. Buli by means of it we 

 have obtained provisional explanations, at 

 least, of many complex phenomena ; while 

 the usefulness of the hypothesis as an aid 

 to further investigation has already been 

 amply demonstrated. Now that we recog- 

 nize the futility of attempting an ultimate 

 explanation of natural phenomena, can we 

 demand more than this of any theory or hy- 

 pothesis ? Let us therefore adopt the new 

 theory in those cases where its adoption 

 leads to clearness and eoncreteness, and 

 make use of it as long as it aids in the ad- 

 vancement of science. As our knowledge 

 increases, the theory will be continually 

 modified and improved. Sooner or later 

 it will doubtless be found insufiScient, and 

 will be abandoned; and something better 



* Wied. Ann., 48, p. 389, 1893. 



t Wied. Ann., 66, p. 353 and 545, 1898. 



X Nature, May 10, 1900. 



