OF THE VIBRATIONS OF AN INVARIABLE PENDULUM. 
217 
thickest. An iron cement, composed of cast iron filings and white lead, was 
then rubbed strongly into the porous parts of the cast iron ; and several coats 
of oil paint were given successively, both to the outside and inside of the 
cylinder. These alterations having been made, the apparatus was again esta- 
blished in front of the clock, and prepared for a second experiment. 
Exp. II. — July 13th ; Molyneux losing 0 S .2 per diem. 
Every thing was arranged on this day as in the first experiment, with the 
exception of the above alterations, and the removal of the telescope for ob- 
serving coincidences nearer the pendulum, from which it was now distant 
1 1 feet. The diaphragm and arc were also placed within the glasses, instead 
of being between the glasses and the clock. The graduated arc was 48 inches 
below the point of suspension, whence the registered arc required to be multi- 
plied by .87 to produce the true arc. The preliminary vibration in air was as 
follows. 
No. of 
Coincid. 
Therm. 
Barom. 
Times of 
Arc registered 
and true Arc. 
Mean 
Interval. 
Correc- 
tion for 
Arc. 
Reduc- 
tion to 
70°. 
Corrected 
Vibrations 
at 70°. 
Disapp. 
Re-app. 
Coincidence. 
1 
22 
70.0 
69-5 
inch. 
29-43 
29.46 
m s 
58 05 
11 43 
m s 
58 12 
12 03 
h m s 
0 58 08.5 
3 11 53.0 
0 / O' 
1 34.5 = 1 22 
0 370. = 0 32 
C3 
OO 
JO w 
to 
s 
+ 1.40 
s 
-0.10 
85950.86 
69-75 
20.445 ; Index + 0.066 ; Reduction to 32° — 0.107 ; = 29.404. 
85950.86 
The air was then withdrawn, and the following observations made. 
No. of 
Coincid. 
Gauge. 
Therm. 
Times of 
Arc registered 
and true Arc. 
Mean 
Interval. 
Correc- 
tion for 
Arc. 
Reduc- 
tion to 
70°. 
Corrected 
Vibrations 
at 70°. 
Disapp. 
Re-app. 
Coincidence. 
1 
19 
32 
59 
149 
inch. 
1.50 
1.70 
1.75 
1.80 
1.80 
68.8 
69.0 
68.8 
68.0 
67.1 
m s 
18 31 
15 13 
39 39 
35 19 
22 31 
m s 
18 38 
15 23 
39 53 
35 39 
23 01 
h m s 
4 18 34.5 
6 15 18 
7 39 46 
10 35 29 
20 22 46 
O' O' 
1 41 = 1 28 
1 16 
1 04.5 
0 44 = 0 38 
0 12 =0 10 
j>389-73 
j 391.52 
+ 1.73 
+ 0.24 
s 
-0.25 
— 0.71 
85959.88 
85959.95 
1.71 
68.34 + 0.75 = 69.09 
85959.915 
2 F 
MDCCCXXIX. 
