1913-14.] Atmospheric Electrical Potential Gradient. 203 
in such districts in the neighbourhood of Leeds, and with a few experi- 
ments designed to suggest an explanation of certain abnormalities, as 
compared with previous records. Our apparatus * comprised a Lutz 
flame collector on an ebonite rod, an Exner electrometer for measuring 
potential differences to 800 volts, and a Braun electrometer for read- 
ings over 800. All measurements were made at a height of 1 metre 
from earth. 
Curve A . — These measurements were made on a grass field near 
Kirkstall Forge, Leeds. The wind was blowing from the forge chimneys 
about 150 yards away ; the tops of the chimneys being a little below the 
A. 
level of the instruments. During forty minutes the potential gradient 
varied rapidly between 720 and 2200 volts per metre. 
On another day the instruments were 350 yards from these chimneys 
in the same direction, and the smoke caused a variation between 300 
and 2250 during thirty-five minutes. A few hours later, owing to a 
change in the wind, most of the smoke blew somewhat to our right, 
and the variations were in consequence only from 120 to 300 during 
twenty minutes. 
On another occasion we were half a mile from the forge in the same 
direction, and during fifty minutes the reading was never below 630. 
At this same spot, with the same wind direction and on two different 
days, the minimal readings were 390 during ninety minutes and 120 
in twenty minutes, depending on the amount of smoke which reached 
the collector. 
* For the loan of the apparatus we are indebted to Prof. J. H. Priestley. 
