S6 Scientific Intelligence. 



violet radiation, infra-red radiation and the Hertz radiations, 

 which according to the electro-magnetic theory of light are an 

 extension of light radiations, are propagated with one and the 

 same velocity. In other words, there is a velocity of propaga- 

 tion common to all kinds of radiation and independent of the 

 wave-length. It is thus, as it were, certain d priori that the 

 N-rays, all of whose properties approach those of light, and 

 which are surely a variety of it, should have the same velocity. 

 This is precisely what the experiments already described in these 

 Archives show. This verification of a fact reasonably sure in 

 advance seems to me not without interest ; it confirms the com- 

 plete unity of character of what we now call the N-rays. — 

 Archives des Sciences, phys. et nat., Geneva, xvii, May, 1904. 



13. Lehrbuch cler JPhysik ; von O. D. Chwolson ; iibersetzt 

 von H. Pflaum. Bd II., pp. xxii + 1056. (Braunschweig: F. 

 Vieweg und Sohn.)— The second volume of this work presents 

 the same admirable qualities as the first volume, which has been 

 previously reviewed in this Journal.* It comprises the subjects 

 of sound and light and is an exhaustive presentation of the 

 phenomena and, so far as is possible with elementary mathemati- 

 cal methods, of the theory also. The descriptive portions are 

 exceedingly clear, the perspective good, and the arrangement so 

 logical that, notwithstanding the great number of details pre- 

 sented, the treatment of the various subjects has a unity some- 

 what rare in works of this character. A very useful feature is 

 the list, at the end of each chapter, of important original papers 

 bearing upon the subjects treated in the chapter. h. a. b. 



14. Applications of the Kinetic Theory ; by W. P. Boynton. 

 pp. x + 288. New York. (The Macmillan Co.)— This is a well- 

 arranged collection of the principal theorems and applications of 

 the Kinetic Theory, in which physical ideas are not lost sight of 

 by over emphasis upon the mathematical details. The treatment 

 is, in the main, elementary and the methods employed are those of 

 the founders of the theory, rather than the more general ones 

 developed by Boltzmann and other recent writers upon the sub- 

 ject. The author has succeeded in giving a fairly complete 

 account of the subject without assuming a very extensive 

 acquaintance, on the part of his readers, with mathematics and 

 mechanics ; he has avoided the discussion of logical subtleties and 

 delicate questions of rigor which occupy much attention at pre- 

 sent, but which the beginner can well afford to do without. The 

 successive chapters deal with ideal gases, gases whose molecules 

 have dimensions, diffusion and viscosity, change of state, the 

 equation of van der Waals, vaporization, liquids, solution, dissocia- 

 tion and condensation, and a summary containing numerical 

 applications, etc. A knowledge of empirical thermodynamics is 

 not assumed, but is given in the text when it is necessary for a 

 comparison between the results of the theory and those of experi- 

 ment. H. A. B. 



* See volume xv, p. 82, Jan. 1903. 



