LOCAL VARIATIONS AND VIBRATIONS OF EARTH’S SURFACE. 6] 
time, and Iam waiting patiently to see when the easterly excursion 
of our transit a is to cease and the return take place. 
You will observe in the azimuth curves that there are some con-. 
siderable Govtations from the mean line, but the determination of 
azimuth cannot be so accurate as the level, because it depends 
upon the positions of stars which are not all accurately known,. 
and the state of the atmosphere at the time of observation, which 
wa us en odin and one is =. to ask was it due to the 
imperections of the instrumen The new instrument is so 
it in azimuth. The instrument was fitted with a screw adjustment 
for azimuth, so that when the error became large the screw was 
used to set it right, and this facility of motion may have been the 
cause of the annual change in azimuth, the changing in tempera- 
; 
change appearing in the corrections is due to an actual change of 
position of the whole instrument. I cannot, aii ie help think- 
ing that perhaps some saieceiiel changes in hills are caused by 
imperfect instruments. In speaking so far of the changes in the 
change which a second of are represents, I ma say that it is 
aves of an inch or 00002. This will serve also to give some idea 
of the delicacy ve the eS and I may add that a change of 
all our idathimente se a rest give rise to many - dba, and show: 
the need for a full investigation of this subject, and it is to 
be hoped that the laws (if any) of these changes will soon be 
determined. 
Sydney Observatory is situated on a sandstone hill which 
forms one of the headlands in the harbour, and on the west side, at 
a distance of 165 feet from the transit instrument, the roe rock has 
bee 4 : i 
the 
sun, but only for part of the afternoon, as the houses 
