ON SEISMOLOGICAL INVESTIGATION. 213 
The differences in temperature which are in degrees Fahrenheit are 
those recorded in the instrument room between about 8 A.M. and 2 p.m. 
Fig. 9 shows tracings from the photograms of diurnal waves observed 
at Shide. The range of motion has varied between 1’’ and 5". Usually 
the Western motion ceased about 10 a.m., from which hour the pendulum 
moved eastwards until about 7 or 8 p.m. The motion from 10 a.m. or noon 
is therefore similar to that which would accompany a decrease in the 
steepness of the open bare down on the eastern side of the pendulum, or 
a rising of the tree and grass covered valley on its western side. The fact 
that the movements were usually pronounced on bright fine days, and but 
Fie. 9.—Diurnal Wave at Shide. 
Motiow Waestvards —» 
feeble or absent when it was dull or wet. suggests the idea that the ob- 
served movements may have been the result of the removal by evaporation 
of different loads from the two sides of the station. The amplitude of the 
daily wave is far from being proportional to the daily range of tempera- 
ture observed near to the instrument. 
From May 24 to June 7 the pendulum gradually moved westwards, 
and during this time the maximum temperature gradually rese from 
60° to 70°, that is to say, the direction of motion has been the same as 
that which takes place whilst the temperature is rising during the day. 
The creeping of the pendulum between the above two dates is in such @ | 
