252 CAPTAIN SABINE ON THE CORRECTION FOR VARIATIONS OF 
Comparing- this result with 85969.33 vibrations at the temperature of 63°.53 
obtained in August 1829, we have 14.25 vibrations per diem corresponding to 
32°.38 of Fahrenheit ; which gives a correction of 0.44 of a vibration per diem 
for each degree of Fahrenheit between 30° and 60°. 
The experiments which I formerly made with two pendulums similar to the 
present, in a chamber artificially heated to between 80° and 90°, gave for the 
correction for each degree of Fahrenheit, respectively for the two pendulums, 
0.432 and 0.430, corresponding to that part of the thermometer scale which is 
included between 45° and 85°. Those results accord well with each other, and 
are somewhat different from that which is now obtained, and which correspond 
to the part of the scale comprised between 30° and 60°. But in the experiments 
in the chamber artificially heated, the fluctuations of temperature, in spite of 
every precaution, were considerable, and rendered the determination of the 
mean temperature more difficult, and probably less exact than in the natural 
temperatures : hence it would be unsafe to conclude in favour of the inference 
to which these facts would otherwise lead, that the correction at high tempera- 
tures is less than at low temperatures, or that the metal expands a smaller pro- 
portion of its length for one degree between 85° and 45°, than for one degree 
between 60° and 30°. 
The experiments at Greenwich were made in those extremes of natural tem- 
perature afforded by the climate, in which a tolerably uniform temperature is 
maintained for several days ; a condition requisite in such delicate determina- 
tions. The clock by Graham was going well on both occasions, and its rate 
was assigned by Mr. Taylor from comparisons with the transit clock of the 
Observatory, with probably as much accuracy as the rates of clocks are ever 
obtained. The thermometer is entitled, by its comparison with those of Mr. 
Daniell and of M. Bessel, to be regarded as one of good authority, having, 
in the absence of a standard thermometer in this country, received the sanction 
of what must be considered the best existing authorities. Every precaution 
was adopted, which the experience I have had in obtaining the rates of pendu- 
lums has suggested, for maintaining a uniform temperature in the apartment. 
The examination of the partial observations will best show the success of these 
precautions. Viewing all these particulars, I regard 0.44 of a vibration per 
diem for eacli degree of Fahrenheit as a result obtained under circumstances 
