1383. 
The electricity generated on Q, was thus at all events less 
than at ordinary temperature. The decrease was 1.3°/,, 1.2°/,, 1.2°/,. 
The influence of the elastic connection falls within the limits of 
errors of observation. In the absolute measurements the connection 
causes a decrease of about 3 °/,. 
Thus we may conclude that the cooling from 290° K. to 80° K. 
causes a decrease of 1.2°/, in the piezo-electric modulus. A further 
cooling from 80° to 20° causes a much smaller change, it appears 
even less than 2°/,,. The importance of this result is perhaps that 
the change in the piezo-electricity by cooling to low temperatures 
seems to take place chiefly above the temperature of liquid air. 
§ 4. Pyro-electricity of quartz. As has already been said, we 
also made some observations on the pyro-electricity of quartz at the 
temperatures of liquid air and hydrogen. The pressure under which 
the liquid round Q, boiled was changed. By the change of tempe- 
rature, which is the consequence thereof, a pyro-electric charge is 
generated on Q,. The deflections of the electrometer were 
le) le) 
for 90 K to 86.5K + 27.5 mm. or per degree + 8.5 mm. mean value 
OR Ae DE ait cerns Bo Be per 
ONE oy PO Ose tena ee ee eB degree 
ne OU) BO ee oe awa! ee EE HE eee 
{e) Ors 
Bias ete SE Geen et rs + 1.4mm: 
POES eG Bn PO. So uss ha ei ARD ae 
between 20.8, and 15.8, + 14.3 (double deflect.) 1.7 „„ 
The deviation 7.8 per degree at the temperatures of liquid oxygen 
1.6 per degree at the temperatures of liquid hydrogen 
has by an increase of temperature the same direction as by a 
stretching of the plate. 
We note that the generated pyro-electric charge is about propor- 
tional to the absolute temperature. 
We wish to record our heartiest thanks to Mr. G. Horst, assistant 
at the physical laboratory, for his assistance at our experiments. 
90* 
