120 
FIFTH REPORT— 1835 . 
per diem, and had therefore no appreciable influence on the re¬ 
sults. 
Cylinder L («). Cylinder L (b). 
Date. 
Hour. 
Time. 
Temp. 
Date. 
Hour. 
Time. 
Temp, j 
h. m. 
s. 
o 
h. m. 
s. 
o 
March 4. 
1 42 
242-64 
54-5 
March 19.* 
11 7 
293-48 
53-6 
1 55 
242-82 
54-5 
11 40 
292-52 
55-0 
8. 
3 46 
242-30 
58-8 
2 42 
294-00 
60-3 
4 4 
242-24 
58-0 
3 5 
293-76 
59-5 
Mean 
242-50 
56-5 
Mean 
293-44 
57-1 
1. 
3 44 
243 96 
82-5 
12 50 
295-24 
80-0 
4 10 
243-96 
83-1 
1 16 
295*20 
83-3 
8. 
2 6 
243-94 
74-5 
Mean 
295-22 
81-6 
Mean 
243-95 
80-0 
The constant coefficient sought is to be calculated from the 
formula 
T — T' 
“ ~ T' (t - t'Y 
in which t and f are the two temperatures, and T and T the 
corresponding times of vibration. We find 
Cyl.L {a). T' = 242"-50, T - T' = l"-45, t - V = 23°*5 
a = -000254 
Cyl. L (b). T' = 293"*44, T - T = 1"*78, t - V = 24°*5 
a = -000248. 
Stopping at the fifth decimal place, then, the coefficient for tem¬ 
perature for both cylinders is *00025. It is to be observed that 
these cylinders were made at the same time, and were therefore 
probably tempered to the same degree ; and to this circumstance 
we may, with much probability, ascribe the close agreement in 
the values of the constant which determines the effects of tem¬ 
perature upon the force of the needle. 
No observations were made to determine directly the effects 
of temperature upon the other needles employed in the course 
of these observations; and, in correcting the results obtained 
with them, the coefficient employed by M. Hansteen, viz.. 
* A series of observations had been made with this cylinder, in the same 
manner and on the same days as those with cyl. L(a); but the results were unsa¬ 
tisfactory, some of them indicating an increase of force with increased tempera¬ 
ture. Such contradictory results have been noticed by many observers, and are 
usually attributed to the disturbing effects of currents of air, determined by ine¬ 
quality of temperature. 
