3 i2 SCOTT'S LAST EXPEDITION 



of chronometers, were made on an average once every fortnight. 

 During the whole of the second year the rate of the standard 

 chronometer varied only from 0-17 second losing to 0-25 second 

 gaining, a very fine performance considering the adverse condi- 

 tions it had to contend against. 



The complete hourly records of auroras, which have been 

 shown to be connected with sun-spot phenomena and with mag- 

 netic storms, should when worked out give data of considerable 

 value, especially when compared with the data collected by Priest- 

 ley on the Northern Party. 



(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 use- 

 less), 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 Yz inch long were continu- 

 ously 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 ob- 

 servations 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. 



(b) 2. Radioactivity of the air. 



Numerous observations on the radium content of the Ant- 

 arctic air were made during the first year, using the same appara- 

 tus as was used for observations on sea air during the voyage of 

 the Terra Nova. As might be expected (dry frozen surfaces 



* ' Atmospheric Electricity over the Ocean,' G. C. Simpson and C. S. Wright, 

 Proc. Roy. Soc., A., Vol. 85, 1911. 



