﻿310 Prof. R. W. Wood on Dijractidn 



when in radioactive equilibrium radium B contributes 

 11*5 per cent, of the ionization and RaC 88'5 per cent. 



hln ~ -97213 XlX 'Zi^-X 1 )(X,-X 1 ) 

 X = l,'2,3 



•885 . . V e- x '* 



' rT^7\T7» AoAqA,. 



■97213 2 3 ^^^(^-^(Xs-^iX^-^i) 

 A= 1,2,3,4 



This equation gives the ionization as measured in a Cook 

 7-ray electroscope. 



Column Y. gives the fall of ionization, reckoned on the 

 same assumption as used in calculating column III., after 

 completely removing from a vessel emanation which had been 

 confined in it for a Ioup; time. 



IN y = e l — -r-7^7^: X 9 \n 



1-0085 2S ^j (\2-\i)0.3-*i) 

 x = 1,2,3 



1-0085 A2A ^ 4 ^ (\ 2 - \ x ) (A, - \0 (\, - Xi)" 



A = 1,2,3,4 



This gives the rate of decay of radium active deposit, 

 completely separated from emanation, as measured with a 

 Cook electroscope. The values of \ assumed in these 

 calculations are the following expressed in (second) -1 : 



^OSxlO" 6 , A 2 = 3'85xl0- 3 , X 3 = 4-33xl0- 4 , X 4 =5-93xl0" 4 . 



XXVII. Diffraction (^ratings with Controlled Groove Form 

 and Abnormal Distribution of Intensity. By R. W. 

 Wood, Professor of Experimental Physics, JoJins Hopkins 

 University *. 



IN the Philosophical Magazine for September 1902 I pub- 

 lished an account of a diffraction grating, ruled on 

 speculum metal, which exhibited a most remarkable distri- 

 bution of intensity of the energy in some of the spectra. 

 The continuous spectrum of a white source was interrupted 

 by bright and dark bands sometimes not over 20 or 30 

 Angstrom units in width, which appeared most distinct 



* Communicated by the Autliur. 



