420 
MR. BAILY ON THE CORRECTION OF 
pumping out the air ancl the lapse of a given interval (for the equalization of 
the temperature which is always disturbed by this process,) but without touch- 
ing any part of the apparatus, I have taken the second series in vacuo : these 
two sets form one comparison. On the conclusion of this series (everything 
remaining the same, and no part of the apparatus being in any way disturbed 
or handled,) I have immediately taken the third series in vacuo : then, after 
letting in the air, and suffering everything to remain undisturbed as before 
for a given time, I have taken the fourth series in free air; which is compared 
with the experiment immediately preceding, and thus forms a second com- 
parison. These four experiments, thus compared, give two results, which are 
in general sufficient for the determination of the quantity sought. But, I have 
frequently repeated the process and taken four other consecutive sets : in 
which case I have usually taken off the glass top, and turned the knife edge, 
end for end, for a reason which I shall more particularly allude to in the 
sequel ; and have then conducted the new series precisely in the same man- 
ner as the former ones. The pendulum has generally been set off, as nearly 
as possible, to the same arc of vibration, and continued for nearly the same 
length of time. In short, I have endeavoured, as much as was in my power, 
to make each pair of experiments which are compared together, as nearly as 
possible under the same circumstances, in order to avoid the chance of any 
error or discordancy arising from any unforeseen cause*. 
First set . — Results with the \\-inch Spheres. 
1) Platina. 
2) Lead. 
3) Brass. 
4) Ivory. 
Exp. 
n 
Exp. 
n 
Exp. 
n 
Exp. 
n 
1—2 
1-873 
17—18 
1-896 
9—10 
1-819 
25—26 
1-879 
3—4 
1-883 
19—20 
1-909 
11—12 
1-817 
27—28 
1-864 
5—6 
1-866 
21—22 
1-840 
13—14 
1-849 
29—30 
1-858 
7-8 
1-904 
23—24 
1-840 
15—16 
1-849 
31—32 
1-886 
Mean = 
1-881 
Mean = 
1-871 
Mean = 
1-834 
Mean = 
1-872 
'llicse remarks apply more especially to the experiments recently made for the express purpose of 
this inquiry. Other experiments, made prior to the present year, without reference to this subject, 
are taken from my observation books, in the order in which they were made. 
