796 
LORD RAYLEIGH ON THE CLARK CELL AS 
very special purposes it will, no doubt, be desirable to protect standard cells from the 
larger temperature-variations, which is very easily done by keeping them in a cellar, 
from which well-insulated wires will convey the E.M.F. to any desired point. As to 
the absolute magnitude of the variations of E.M.F. with temperature, it may be worth 
while to recall that they are about the double of those experienced by German silver 
resistances. 
§ 54. A good many special experiments have been tried with cells variously 
constructed, in order to elucidate as far as possible the behaviour of Clark’s. Two of 
these, labelled H (1, ^), H (1, ^), were referred to in a short communication to the 
British Association at Montreal, # and have been observed at intervals since, with 
results which are, I think, of interest. In these cells, the legs representing the zincs 
were charged with a strong! but fluid amalgam of zinc and mercury ; so that if the 
other legs had been charged with pure mercury and paste of mercurous sulphate, an 
ordinary Clark would have resulted. This, however, was not done. No paste at all 
was used, and in place of pure mercury a dilute amalgam was substituted—in H (1, 
one obtained by diluting the strong amalgam with its own volume of pure mercury, 
and in H (1, one containing one volume of strong amalgam to three volumes of pure 
mercury. The cells were filled up, as usual, with zinc sulphate solution. 
The electromotive forces, expressed as fractions of No. 1, are recorded in the 
adjoining table (XVII.). It is clear that the E.M.F. rises rapidly with temperature— 
something like 30 per cent, for 15° F. The large amount of this variation, and the fact 
of its taking place in the opposite direction to that followed by Clark’s, are very 
remarkable. 
Table XVII. 
Date, 1834. 
Temperature. 
(Fakr.) 
H (l, !). 
H (l, 1). 
Date, 1885. 
Tem'erature. 
(Fahr.) 
H (1, i) 
H (l, i). 
July 21 . . . 
0 
•0041 
Jan. 2 . 
O 
•0033 
•0083 
22 
,, . 
. , 
•0041 
„ 14. • . 
•0031 
•0081 
„ 23. . . 
. . 
•0041 
Aug. 3 . 
63 
■0044 
•0095 
„ 24. . . 
•0041 
Sept. 5 . 
63 
•0042 
•0095 
„ 29. . . 
•0040 
•0091 
Nov. 6 . . . 
52 
•0034 
•0083 
. „ 30. . . 
. , 
•0040 
■0u91 
„ 12. . . 
56 
•0039 
•0086 
Aug. 6 . . . 
67 
"0044 
•0096 
27 
67 
•0044 
•0093 
Sept. 4 . . i 
62 
•0041 
•0093 
Dec. 2 . . . 
51 
•0034 
•0084 
Oct. 8 . . 
63 
•0040 
•0093 
„ 28. . . 
59 
■0037 
•0090 
Nov. 17 . . . 
. » 
•0036 
•0087 
Dec. 5 . . . 
•0037 
■0089 
It would appear that, apart from changes of temperature, the cells have retained 
their E.M.F. tolerably constant for more than a year and a half-—a result which could 
* B. A. Rep., 1884, p. 651. 
f As to what is to be regarded as strong, more facts 'will presently be given. 
