[WRiGHTj VARIATIONS IN THE CONDUCTIVITY OF AIR 9S 



TABLE V. 

 Mar. 6th. ' 



qo= Number of ions per cc. per sec. reduced to zero centigrade. 



This result seemed somewhat surprising in view of the fact that 

 Prof. McLennan had obtained the same numbers repeatedly during a 

 period of over six months. As the experiments made by the writer 

 with the three lead cylinders were carried out in a room in the new 

 physical laboratory, and those by him in one in the older building, it 

 was thought well to make a redetermination in the latter, but, on doing 

 this, it was found that a slightly lower value even was obtained for the 

 ionization in the measurements taken in this room than in those in 

 tlie new laboratory. 



Although the experiments were made in a room supposed to be 

 free, or far removed, from any active substances, it seems probable that 

 there was in the old department, or in the rooms adjacent, some unob- 

 served source of radiation present 'during Prof. McLennan's investiga- 

 tion which was absent during the measurements made by the writer, 

 and this impurity was very probably removed when the old laboratory 

 was vacated by the Department of Physics and adapted to other purposes. 



It might be pointed out that the lowest value for "q" hitherto 

 recorded for the ionization in a lead cylinder, even with this possible 

 additional influence is that of 23 ions per cc. per sec, given by Profes- 

 sor McLennan. The present value of 15, obtained with this cylinder, 

 là still lower, and would seem to indicate that we possessed in this lead 

 receiver one which contained little if any impurity. It was, therefore, 

 especially suitable, if proper screens could be found, for the investiga- 

 tion of any intrinsic activity associated with the metal lead itself. 



IV. Preliminary Observations on Conductivity. 



(a)— General conditions of the different experiments- 

 It has been noted by Prof. McLennan and other observers that 

 when a metallic receiver has been thoroughly scoured with emery or 

 glass paper in order to remove any active coating which may have been 

 deposited on its surface by exposure to the atmosphere, and after being 

 washed with hydrochloric acid, ammonia, alcohol and distilled water, 



