VIBRATIONS MADE BY AN INVARIABLE PENDULUM. 
241 
rate of this clock during the experiments was furnished by Lieut. Nehus of the 
Royal Danish Engineers, assistant to M. Schumacher in the Trigonometrical 
Survey of Denmark ; who for that purpose compared it daily with the transit 
clock of the Altona Observatory at those hours which were not suitable for 
giving its rate whilst the pendulum was in vibration. The heights of the ba- 
rometer were furnished by M. Peterson, assistant in the Observatory, from 
M. Schumacher’s standard barometer. The height of the pendulum above the 
level of the sea in M. Schumacher’s house was 15.1 toises. 
Having an opportunity on this occasion of comparing the thermometer 
graduated in 1823 by Mr. Daniell and myself, and employed in the present 
experiments, as well as in all the former determinations which I have made 
with invariable pendulums, with a standard thermometer presented by 
M. Bessel to M. Schumacher, I was anxious to avail myself of it ; and M. Schu- 
macher with great kindness undertook himself to make the comparison. The 
thermometers were compared by immersing the bulbs to the same level in 
water warmed very gradually in a chronometer stove by means of a small night 
lamp, and suffered again to cool ; the thermometers being compared both in 
the ascending and descending temperatures. I copy the following particulars 
of the comparison from M. Schumacher’s memorandum. 
“ B are the readings of M. Bessel’s thermometer. 
E. B. . . are the equations of M. Bessel’s thermometer. 
R. T.. . are the real temperatures. 
S are the readings of M. Sabine’s thermometer. 
E. S. . . are the equations of M. Sabine’s thermometer. 
1828. 
Oct. 20. 
h 
m 
s. 
B. 
E. B. 
R. T. 
E. S. 
1 
38 p.m. 
. 59.6 
. 60.0 
. -0.20 
. 59.80 . 
+ 0.20 
1 
43 
. 60.0 
. 60.5 
. -0.20 
. 60.30 . 
+ 0.30 
2 
33 
. 65.0 
. 65.3 
. -0.23 
. 65.07 • 
+ 0.07 
3 
24 
. 70.2 
. 70.6 
. -0.26 
. 70.34 . 
+ 0.14 
5 
0 
• 78.7 
. 81.1 
. -0.32 
. 80.78 
7 
0 
. 86.35 
. 86.7 
. -0.38 
. 86.32 . 
-0.02 
9 
25 
. 91.75 
. 92.1 
. -0.44 
. 91.66 . 
-0.09 
11 
47 
. 94.60 
. 95.3 
. -0.47 
. 94.83 . 
+ 0.23 
2 i 2 
