Chemistry and Physics. 589 



ity corresponding, by the y-i'ay method, to 6 mg. of radium 

 bromide. The negative shows six strong spectral lines, one 

 (undeviated) for the a-ray pencil and hve for the /3-ray pencils. 

 The line for the slowest /3-rays is resolved into two distinct com- 

 ponents, a fact which the earlier work did not bring out. A 

 photograph taken with a stronger magnetic field showed two addi- 

 tional but weak lines, and this leads the authors to remark : "It 

 is probable that, with stronger preparations and greater resolving 

 power, the existence of still other weak /3-rays could be demon- 

 strated." On the other hand, the improved experimental con- 

 ditions did not essentially change the continuity of the broad, 

 diffuse band produced by the swifter /3-rays. 



Since, as is well known, mesothorium 2 has a half-value 

 period of 6*2 hours, the authors thought that it ought to be 

 possible to show photographically the growth of thorium X, 

 thorium emanation, and the resulting active deposit. In order to 

 test this point, a second exposure was made, 24 hours later, to 

 the same active wire mentioned above. A new line, ascribed to 

 thorium X, shows very distinctly on this negative, whereas the 

 spectrum of mesothorium 2 is appreciably fainter. A third expo- 

 sure of twelve hours duration was made eight days after the first. 

 It contains no lines of mesothorium 2, it verifies the second neg- 

 ative, and it shows a second, less-deviated, fainter line of thorium 

 X. Also, a still less deviated line of thorium A may be seen in 

 the reproduction. The photographs of this set are scientifically 

 beautiful and very instructive. 



The second division of the paper deals with the /3-rays from 

 the active deposit of thorium. The details of this section will be 

 passed over in order to quote the third division, in which are 

 collected the latest results of this work. Mesothorium 2 gives rise 

 to swift /3-rays, exceeding 0*7 of the speed of light. In addition 

 there are two weak lines corresponding to speeds of 0*66 and 0-60, 

 and five strong /3-ray pencils of speeds # 57, 0*50, 0*43, 0*39, and 

 0-37. Thorium X gives 0*51 " weak" and 0'47 "strong." Tho- 

 rium A gives 0*72 weak and 0*63 very strong. Th (B + C+D) 

 has fast /3-rays over 0*72 of 3X10 10 cm /sec together with 0-36 weak 

 and 0*29 strong. — Physlkal. Ztschr., April 1, 1912. h. s. u. 



7. Applied Physics for /Secondary Schools ; V. D. Hawkins. 

 Pp. ix, 199. Xew York, 1912 (Longmans, Green & Co.).^The 

 author is of the opinion that modern text-books on elementary 

 physics are too mathematical and far too difficult to be mastered 

 in one year by the average high school pupil. Therefore he has 

 written a very elementary book which is based on the belief that 

 the best methods of teaching the subject are as follows : " 1. By 

 a brief text for all of which the pupil will be held responsible, 

 and, 2. By the addition of many interesting local applications to 

 be supplied by both teachers and pupils." The diagrams are well 

 drawn and the topics selected are very interesting. h. s. u. 



8. Pie Messung vertikaler Luflstromungen / by Paul Ltjde- 

 wig. Pp. 30, with 23 text-figures and 4 charts. Leipzig, 1911 



