Manchester Memoirs, Vol. xlviii. (1904's No. \%. 5 



the air current is known, and as e is known to be very 

 approximately 3'4X lo"'^ a may be calculated. 



Four observations taken during the last few days may 

 serve as illustrations, but I do not attach great value to 

 the actual numbers as I have had no opportunity yet of 

 checking some of the constants of the instruments, and 

 there is also some unexplained systematic difference 

 depending on the quantity of radium employed in the 

 measurement. 



The places of observations are 



i? = A field near Rochdale. The observations having 



been taken on Sunday there was no smoke from 



factory chimneys. 

 O = Flat roof by the side of the Observatory on the top of 



the buildings of the Physical Laboratories. 

 S=K large room (36 x 24 feet) on the ground floor of the 



Laboratory. 



The value of a for dust-free air was determined with 

 the same apparatus to be i*i x lO"^ for dust-free fairly 

 dry air, agreeing closely with Townsend's value. 



Date. 



Place. 



Weather. 



a,. 



n. 



■III. 



Feb. 28/04 



R 



Snowing at inter- 

 vals, with spells 

 of sunshine. 

 East wind 



3-28 X 10"'^ 



2370 



18-4 



„ 29/04, morning 







Cold — bright — 

 gusty. East 

 wind 



2*96 



3600 



38-5 



„ 29, afternoon... 







Cold— dull. 

 East wind... 



2-86 



3660 



38-3 





s 





2*14 



2370 



12 



)) ■^y 





