13581 
connection with the earth. The electrometer needle was kept at a 
constant potential of 120 volts. 
The quartz plate Q, was suspended in an earthed meta! case and 
carried a scale pan, on which weights could be placed, in order to 
stretch the plate; Q, was put in a Dewar glass; its lower end was 
fastened in a brass support, which was carried by the cap of the 
vacuum vessel; the uppermost end was suspended by a brass rod 
to one arm of a balance, whose other arm carried a scale, which 
could be loaded with weights. In order to be able to close the vessel 
hermetically (which was quite necessary), and at the same time make 
the free movement of the rod through the cover possible, it was 
simplest, for these preliminary measurements, to use an elastic india 
rubber tube which closed round the rod and the tube in the cap. 
As we shall see this had only a slight effect on the relative measurements. 
Within the glass the quartz plate and the support were surrounded 
by a brass net. in connection with the earth. 
The measurements were made in the following way: first the 
plate Q, was stretched by a weight (500 gr.) and the deviation of 
the electrometer needle was observed. Then this plate was earthed, 
and when the connection with the earth was broken, the weight 
was removed and the deviation of the electrometer to the other 
side was observed. The sum of these deviations is proportional to 
the quantity of electricity generated. Then the electricity which was 
generated on Q, was measured in the same way. Immediately before 
and after the measurements the electrometer was calibrated with a 
Weston element. The sensibility changed very little. 
The insulation was generally very good, so that there was seldom 
any need of making corrections for leakage. 
Always five or seven turnings of the electrometer needle were 
observed. From these the eventual corrections for incomplete insula- 
tion could be calculated. 
§ 3. Results. I. Both the quartz plates at room temperature 
ey == 2790" K.). 
The deflections were 
mean values 
Q, 126.7 gi die 127.0 127.6 127.4 1272 
Q, 163.7 164.0 163.6 163.2 163.3 163.6 
The Weston element (1.018 Volt) gave 34.4. 
The capacity of the electrometer, of the connections to Q, and 
of Q, itself was about 150 ecm.; that of the connection to Q, and 
of Q, was about 100 em. By the cooling of Q, its capacity changes. 
90 
Procecdizes Royal Acad. Aislerdam. Vol. XIV. 
