﻿Notices respecting New Books. 445 



Uranium I. therefore, which has a period of 5 x 10 9 years, 

 emits a particles of range 2*5 cm. in air at atmospheric 

 pressure and at 15° C, and is followed by another a-ray 

 product, uranium II, which has a period of about 2 X 10 6 

 years and emits a. particles of range 2'9 cm. It is thus clear 

 that in purified uranium preparations two successive a-ray 

 products are present, differing in atomic weight by 4 units. 

 These products must be very closely allied in chemical 

 properties, for the experiments of many observers, amongst 

 whom may be mentioned Boltwood and Soddy, have shown 

 that it is impossible to reduce the a-ray activity of uranium 

 by any chemical methods. A similar striking chemical 

 affinity has been observed in the two elements thorium and 

 ionium and also in a few other cases. Since the ratio of the 

 two transformation constants of the two products in uranium 

 is of the order of 10 3 , the amount of uranium II. in a gram of 

 uranium is about one milligram. The presence of this small 

 quantity of uranium II., differing only by 4 units from the 

 atomic weight of uranium (238*5), can only affect a de- 

 termination of the latter in the third decimal place. 



Taking the range of the a particles from ionium as 

 3-00 cm. at 15° 0. ( = 2'84 cm. at 0°C), we find by inter- 

 polation from fig. 3 that it has a period of about 200,000 

 years, instead of the million years previously deduced. 



Using the figures given in our previous paper, Svvinne * 

 has recently shown that the relation between range and 

 transformation constant can be expressed in another form, 

 but we postpone any discussion of this until the experiments 

 on the ranges of the ol particles from the products in the 

 thorium series which are now in progress have been com- 

 pleted. 



We wish to express our thanks to Prof. Rutherford for his 

 kind interest and help in these experiments. 



The Victoria University, Manchester, 

 Physical Laboratories. 



XLI. Notices respecting New Books. 

 A Course of Plane Geometry for Advanced Students. Part II. 

 By Clement V. Duhell, MM Macmillan & Co. : London 

 1910. 



TN the first part of this important work Mr. Durell dealt with the 

 - 1 - geometry of the straight line and circle. He now continues his 

 method of treatment to the geometry of the conic. The nature ol 

 the treatment cannot be better described than in the following 

 * R, Swinne, Phys. Zvitschr. xiii. p. 14 (1912). 



