i9"] THE ELECTRICAL INSTRUMENTS 277 
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 measure- 
ments is a modified type of the old gold-leaf electroscope. 
The measurement 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 move- 
ment 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 - 1 8°. 
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 
* The white dogs. 
