4S4 
SCOTT'S LAST EXPEDITION 
(b) Atmospheric electricity, 
(b) I. Potential gradient. 
During the whole of the first year and part of the 
second (until the almost continuous blizzards made 
observations useless) records of the potential gradient 
of the atmosphere were made in the usual way by use 
of the self-recording Benndorff electrometers. Owing 
to the mechanical difficulties of such work in cold regions, 
recourse was had to the lately discovered element ionium 
as a collector of the air potential, this substance being 
furnished by the great kindness of Prof. Giesel. 
An interesting effect, noticed almost immediately on 
setting up the apparatus, was that in high winds, even 
when there was only the slightest amount of very low 
drift, the collector became charged to such an extent that 
sparks | inch long were continuously emitted by the 
charged system. 
In order to obtain an estimate of the mean absolute 
value of the earth's electrostatic field in the Antarctic, 
comparison eye observations were undertaken over the 
level surface of the sea ice, similar to those undertaken 
at Melbourne for determination of the absolute value of 
the potential gradient over the sea.* These observations 
gave for the Antarctic a mean value of the same order 
as those obtained in other latitudes and over the sea, 
(J?) 2. Radioactivity of the air. 
Numerous observations on the radium content of 
the Antarctic air were made during the first year, using 
the same apparatus as was used for observations on sea 
♦ ' Atmospheric Electricity over the Ocean/ G. C. Simpson and 
C. S. Wright, Pyoc. Hoy. Soc, A., vol. 85, \gii. 
