196 PROFESSOR E. RUTHERFORD ON THE 



The close agreement of the curve LL with the theoretical curve deduced on the 

 assumption that there are two changes, the first of which does not emit rays, shows 

 that the change of radium B into C does not emit a rays. In a similar way, as in the 

 curve I, fig. 11, the curve LL may be analysed into its two components represented by 

 the two curves CC and BB. The curve CO represents the activity supplied by the 

 matter C present at the moment of removal. The curve BB represents the activity 

 resulting from the change B into C and is identical with the corresponding curve in 

 fig. 11. Using the same line of reasoning as before, we may thus conclude that the 

 change of B into C is not accompanied by a rays. It has already been shown that it 

 does not give rise to ft rays, and the identity of the ft and y-ray curves show that it 

 does not give rise to y rays. The change B into C is thus a ' rayless ' change, while 

 the change C into D gives rise to all three kinds of rays. 



An analysis of the decay of the excited activity of radium thus shows that three 

 distinct rapid changes occur in the deposited matter, viz. : 



(1) The matter A, derived from the change in the emanation, is half transformed 



in 3 minutes and is accompanied by a rays alone ; 



(2) The matter B is half transformed in 21 minutes and gives rise to no 



ionizing rays ; 



(3) The matter C is half transformed in 28 minutes and is accompanied by 



a, ^8 and y rays ; 



(4) A fourth very slow change, which will be discussed later (section 23). 



19. Equations Representing the Activity Curves. The equations representing the 

 variation of activity with time are for convenience collected below, where 

 \! = 3'8 X 10- 3 , X 2 = 3-10 X 10-*, X 3 = 4-13 X 10-*:- 



(1) Short exposure : activity measured by ft rays, 



1,/lT =10-3 (e~* - e~*), 

 where I T is the maximum value of the activity ; 



(2) Long exposure : activity measured by ft rays, 



where I is the initial value ; 



(3) Any time of exposure T : activity measured by the ft rays, 



I, _ aer* be'* 

 Io = -& 



where 



a = b = 



(4) Activity measured by a rays : long time of exposure, 

 J< = 1 e ~* + (4-3 e-^' - 3'3 ?-). 



