166 
DR. H. T. BARNES ON THE CAPACITY FOR HEAT OF WATER 
when immersed at a temperature above or below 15°, the possibility of the zinc rod 
being at a slightly different temperature to that of the cell is thinkable, and would 
act in such a way as to make the positive change between 15° and 0°, as well as the 
negative change between 15° and 30°, appear smaller than the true values. 
Later on in the year, on September 10, a comparison was made of the old crystal 
cells with two of the original sealed cells, made in 1896, and at that time still in the 
possession of the laboratory, as well as three new sealed cells. This comparison is 
given in Table III. and gives the differences in millivolts between each sealed cell and 
the mean of the old crystal cells, the comparisons of which were given in Table I. 
Table III.—Comparison of Sealed Cells with Old “ Crystal ” Cells. 
Cell. 
Difference from mean of old cells. 
Si. 
S 5 . 
Sn. 
nS n . 
S 12 . . . . . 
+ 0 • 18 mv. ) 
+ 0 ' 34 ” ' Mean 
+ 0-20 „ y 90 
+ 0-23 „ | +°’23mv. 
+ 0'21 „ J 
The agreement of the new sealed cells with the old sealed cells is good, but both 
show that the mean of the old crystal cells is too low. This makes the mean of the 
sealed cells, on comparing Tables II. and III., agree with the mean of the inverted 
cells to '06 mv. 
A comparison of the six crystal cells X 1} X 2 , X 3 , X 5 , X 10 , and X n , with six of the 
newer crystal cells made by the students in 1899, was made on March 14, 1900, 
when the last comparison of the old crystal cells given in Table I. was obtained. In 
Table IV. this comparison of the six new cells is given, and the differences expressed 
in millivolts from the mean. Cell X 2 is included, and differenced from, but not 
included, in the mean. 
Table IV.—-Comparison of New “ Crystal ” Cells, on March 14, 1900. 
Cell. 
Difference from mean. 
x 21 .... 
- 0 • 24 mv. 
x 23 .... 
+ 0-05 „ 
X 27 .... 
-0-05 „ 
X 99 . . . . 
+ 0-05 „ 
X 31 . . . . 
+ 0-11 „ 
X 33 . . . . 
+ 0 ■ 08 ,, 
x 2 . . . . 
-0-17 „ 
During the winter previous, when all these new cells were made, the tests on 
the temperature changes between 15° and 0°, and 15° and 30° gave the mean 
