29 207 



fened constructing an even curve showing the progress of a in the first hour, by 

 means of vahies of a obtained at fixed points of time. Then I have from the 

 curve deduced the mean values of a corresponding to 10, 20, 30, 40, 50, and 60 

 minutes after the active gas was introduced into the ionisation vessel. Every one 

 of these values of a therefore could be employed in determining the amount of 

 emanation in the gas. But in order still further to eliminate possible errors in the 

 measurements, I have, instead of using one of these six values, used their mean 

 value J 



«m = ^ («10 + «20 + «30 + «40 + «50 + «60) 



which also, as may be easily shown, is proportionate to the amount of the emana- 

 tion. For if the amount of emanation. A', at the above fixed points of time 

 produces an ionisation represented by a'^^, a^.^, a'^, etc., while another amount of 



etc., we get 

 the relations : — 



A^ 



A" 



By letting A be equal to a„„ the emanation is expressed in an arbitrary unit, besides 

 which, it is dependent on the apparatus used. Therefore it was very important 

 for me to find a unit for the emanation that was well defined and could be easily 

 reproduced, so that the results of my experiments at any time could be compared 

 with results of other scientists in the same domain. The simplest way out of the 

 difficulty would have been to make use of the unit that St. Meyer and H. Mache ' 

 have proposed for use in expressing the radium emanation contained in spring gases. 

 According to their definition, the unit is the amount of emanation that by means 

 of its ionising power sets free per second an electrostatic unit of positive electricity 

 and an equal quantity of negative electricity. The emanation is calculated per 

 litre of spring gases. 



My measurements could be easily expressed in terms corresponding to this 

 definition of the emanation unit. In the first few seconds after the introduction 

 of the gas liberated from the disintegration products of the emanation, the ionisa- 

 tion in the ionisation chamber is due solely to the emanation. Therefore if a, 

 in equation (6), is replaced by Oo, then E in the same equation is simply the 

 emanation expressed in the unit proposed by St. Meyer and H. Mache, or 



^ = ^= 3000000 "0 = 4.73 xl0-0a„. (7) 



Nevertheless I have not used this emanation unit in the compulation of my experi- 

 ments because I am of the opinion that the ionisation caused by the emanation 

 is not only dependent on the amount of the emanation, but to a certain extent is 



' Phys. Zeitsclir. 6, 693, 1905. 



