COMPARISON OF THERMOMETERS. 
779 
Comparisons of C, B, D in July 1855. 
No. of comparisons. 
C. 
B. 
D. 
10 
19-884 
20-258 
19-967 
10 
20-535 
20-885 
20-616 
Mean of 20 comparisons .. 
. 20-209 
20-571 
20-291 
Hence, at 20°, B — C=+0-362, B— D=+0-280. 
Also, by a mean of 11 comparisons at 20°, K— C=+0‘107j K — D=4-0'040. By 
30 comparisons at 18°, and 10 at 21°, B — K=4-0'261. Therefore B — C=+0'368, 
B— D=+0’301. The resulting mean value of the depression of the zero of B is 
0°'12. The value deduced from the observations of the freezing-point is 0°T3. 
Comparisons of C, B, D in September 1846. 
No. of comparisons. 
c. 
B. 
D. 
10 
26-551 
26-884 
26-750 
10 
25-385 
25-695 
25-516 
10 
24-401 
24-670 
24-531 
10 
23-448 
23-725 
23-577 
10 
26-634 
26-949 
26-796 
10 
23-646 
23-940 
23-774 
Mean of 60 comparisons .. 
. 25-011 
25-311 
25-157 
Hence, at 25°, B — 
C=+0-30, 
B-D= 
+0-153. 
By a mean of 16 comparisons of C, B, D between 23°'9 and 26°‘2, in July 1855, 
their corresponding readings were 
C. B. D. 
25-081 25-487 25*204 
Hence, at 25°, B-C=:+0-406, B-D=+0-283. 
Also, 17 comparisons of C, K, D, gave K— C=+0T24, K— D= — 0‘007, and 10 com- 
parisons of B, K, gave B — K=+0’286. Therefore B — C= -f-0'410, B— D = -f0‘279. 
The resulting mean value of the depression of the zero of B is 0°T2, the same as its 
calculated value. 
The thermometers G, L have arbitrary scales, the divisions of which are traced on 
the tubes vvith a diamond point at every tenth of an inch. The parts of the scales 
of G, L, as well as those of B, C, D, K, are subdivided to hundredths of an inch by 
sliding scales of glass. The division of the sliding scale which is brought into appa- 
rent coincidence with the extremity of the thread of mercury, is viewed through a 
hole in a plate of brass attached to a very light brass frame which carries the scale, 
so that the direction of vision may be perpendieular to the axis of the tube. 'I'he 
hundredths of an inch are subdivided by estimation. 
5 K 
MDCCCLVI. 
