192 SCOTT'S LAST EXPEDITION [May 



measurement of the other by means of reduction in the length 

 of the quartz fibre. The object of this is to continue the record 

 in snowstorms, &c., when the potential difference of air and 

 earth is very great. The instruments are kept charged with 

 batteries of small Daniels cells. The clocks are controlled by 

 a master clock. 



The instrument available for radio-activity measurements is 

 a modified type of the old gold-leaf electroscope. The measure- 

 ment is made by the mutual repulsion of quartz fibres acting 

 against a spring — the extent of the repulsion is very clearly 

 shown against a scale magnified by a telescope. 



The measurements to be made with instrument are various: 



The ionization of the air. A length of wire charged with 

 2000 volts (negative) is exposed to the air for several hours. 

 It is then coiled on a frame and its rate of discharge measured 

 by the electroscope. 



The radio-activity of the various rocks of our neighbour- 

 hood; this by direct measurement of the rock. 



The conductivity of the air, that is, the relative movement 

 of ions in the air; by movement of air past charged surface. 

 Rate of absorption of -\- and — ions is measured, the negative 

 ion travelling faster than the positive. 



Wednesday, May 17. — For the first time this season we 

 have a rise of temperature with a southerly wind. The wind 

 force has been about 30 since yesterday evening; the air is 

 fairly full of snow and the temperature has risen to - 6° from 

 -18°. 



I heard one of the dogs barking in the middle of the night, 

 and on inquiry learned that it was one of the * Serais,' * that he 

 seemed to have something wrong w^ith his hind leg, and that 

 he had been put under shelter. This morning the poor brute 

 was found dead. 



I'm afraid we can place but little reliance on our dog teams 

 and reflect ruefully on the misplaced confidence with which I 

 regarded the provision of our transport. Well, one must suffer 

 for errors of judgment. 



This afternoon Wilson held a post-mortem on the dog; he 

 could find no suflicient cause of death. This is the third animal 

 that has died at winter quarters without apparent cause. Wilson, 



* The white dogs. 



