396 Notices respecting New Books. 



the value of K should probably be taken as 3'8 x 10 9 , as the 

 greater part of the soft 7 radiation due to radium B would 

 not pass from the earth, but undergo absorption in tbe soil. 



On the other hand, if the heating effect of the 7 radiation 

 from radium and its products is to be calculated from the 

 resulting ionization, then obviously tbe effects of all the soft 

 7 radiation should be included, and the whole calculation 

 becomes a difficult one. 



An addition of about five per cent, should be made to the 

 above figures if the International radium standard be adopted, 

 so that then K = 4"0x 10 9 and N = 8'4xl0 14 . 



Summary. 



A redetermination has been made of the total number of 

 ions which can be produced in air by the 7 rays from a 

 gramme of radium and its subsequent products. The number 

 found is 8*4 x 10 14 , in close agreement with previous deter- 

 minations, but the value does not include the number 

 produced by the easily absorbed 7 rays. 



XLIII. Notices respecting New Books. 



Annals of the Astrophysical Observatory of the Smithsonian Institution. 

 Volume III. By C. G. Abbot, Director, E. E. Eowle and 

 L. B. Aldrioh. Quarto. Pp. xi + 211. Washington, 1913. 



THIS volume gives a survey of the operations of the Smithsonian 

 Institution directed towards the determination of the ' : Solar 

 constant of radiation" since July 1907. Extensive observations 

 have been made at Washington, on Mount Wilson and Mount 

 Whitney, both in California, and at Basso ur, Algeria. The volume 

 describes in detail the instruments, pyrheliometers and bolometers 

 ot various types, explains the processes ot reduc ion adopted, ;ind 

 gives tables of results. The combination of observations from 

 nearly sea-level at Washington, 5700 feet on Mount Wilson, and 

 14500 feet on Mount Whitney, affords a cheek on the corrections 

 applied for absorption by the earth's atmosphere ; while the 

 comparison of American and Algerian results enables conclusions 

 to be drawn as to the general character of the phenomena. It 

 is claimed that the scale of measurement of radiation and the 

 value of the " solar constant" of radiation have been established to 

 w 7 ithin 1 per cent. Eor the " solar constant " the mean value 

 derived from the observation of the 11 years 1902-1912 is 1*932 

 calories per sq. cm. per minute. The condition is, however, 

 drawn that the sun's radiation is not really constant, " but varies, 

 with an irregular periodicity of from 7 to 10 days on the average, 

 and with irregular amounts seldom if ever exceeding 10 per cent. " 

 This is a result of such far reaching importance that confirmation 

 from an absolutely independent source will probably he found 

 necessary to secure universal acceptance 



