TEMPERATURE OF AN INVARIABLE PENDULUM. 
253 
of a very favourable nature, and as not likely to be surpassed in the confidence 
which may be due to it, until by a better command of artificial temperatures 
the experiments can be made to include, with tolerable certainty of determina- 
tion, a greater difference of temperature than is afforded by the natural climate 
of this country. 
As the many invariable pendulums which have been employed of late years 
by British observers have all been made of the same kind of brass, it is pro- 
bable that the same correction for temperature will apply equally to all. 
When, as in ordinary cases, the differences of temperature between observa- 
tions designed to be comparative amount only to a few degrees, the probable 
error which may be incurred by employing the correction 0.44 for each degree 
as now determined, can only be very inconsiderable : but when the differences 
of temperature amount to 50°, which is a case of actual experience in pendulum 
observations, the question of whether 0.43 or 0.44, for example, be the more 
correct value, involves an uncertainty in the ultimate result of no less than 
half a vibration a day. It seems therefore desirable, for the sake of experiments, 
which are becoming greatly multiplied, and which are daily increasing in 
accuracy, that means should be devised of obtaining the rates of pendulums in 
artificial temperatures, embracing a wider range than the natural temperatures, 
but capable of being determined with equal accuracy. 
Table C. — Vibrations of Pendulum 12 at Greenwich, December 1829, and 
January 1830, on the fixed iron support in the Pendulum room. The Baro- 
meter employed was the standard barometer of the Royal Observatory ; the 
Thermometer was Captain Sabine’s standard thermometer ; the Arc was di- 
stant 60 inches from the point of suspension, and was divided into degrees, 
each of 0.8 of an inch in length ; the registered arc therefore multiplied by 
0.764, gives degrees of the true arc of vibration. 
ExP. 1. Dec. 29th. Clock making 86552.75 Vibrations. Barom. |< 3 o'gooj' 30. 212 27°. 
No. of 
Coincid. 
Therm. 
Times of 
Registered 
Arc. 
True 
Arc. 
Mean 
Therm. 
Mean 
Interval. 
Correc- 
tion for 
Arc. 
Vibrations in 
24 hours Mean 
Solar Time. 
Reapp. 
Disapp. 
Coincidence. 
1 
53 
28.6 
28.4 
m s 
15 37 
34 38 
m s 
15 42 
34 54 
h m s 
1 15 39.5 
5 34 46 
0.84 
0.24 
0.64 
0.18 
| 28.5 
s 
298.97 
s 
+ 0.24 
85973.99 
