180 
DE. H. T. BAENES ON THE CAPACITY FOE HEAT OF WATER- 
set by means of the temperature coefficient found from the tests given in Table X. 
Most of the comparisons up to September 10, 1898, were made by Mr. Sheffield, 
and from that date on, by myself. The maximum variation from the mean is 
5 X 10 ~ 5 ohm, and is within the limits of error for a series of comparisons 
such as these. As a rule the agreement is very much closer than this. Taking 
the value of 4086 as equal to 1’00045 true ohms at 20° O. in place of the value 
assumed for calculation in the table, we find Coil 1, 1‘00132 -f- ‘00043 = 1 00175 
true ohms at 20° C., and Coil 2, 1‘00043 ohms. At any other temperature the 
coefficients +‘000250 for Coil 1, and ‘000246 for Coil 2, are used, which were 
obtained from the experiments detailed in Table X. 
The value of the two 1-ohms in parallel is very easily determined on a small slide- 
rule, by assuming the ohms equal to (1 + d x ) and (1 + cl. 2 ) respectively, where + 
and + are equal to the small differences from unity, then 
( 1 + dj) (1 4 A) __ _ jr (A + A) 
(1 + A) + (1 + A) 2 + + + + 
neglecting products and powers of d x and oh. 
At 20° C. the value of the fraction is 
R = ‘5 + = '500544 ohm. 
At 10° C., when No. 1 is equal to (1 — ‘00077), and No. 2 (1 — ‘00205), 
R = ’ 5 - = ' 499294 ohm - 
We may accept then for calculation the most probable value of the two platinum- 
silver ohms in parallel to be 
‘500544 true ohm at 20° C., ‘499294 true ohm at 10° C., 
where one true ohm = 1‘01358 B.A, unit, as given in all the certificates of the 
standard ohms. 
Current Heating. —It is a matter of importance to determine the true resistance 
of the two coils when the maximum current used in these experiments was passed 
through. For the largest flows of water, when the largest heating current was 
required, this amounted to 8 amperes. This current was divided between eight 
•4-m ill im. platinum-silver wires immersed bare for their entire length, about 1 metre, 
in oil, which was vigorously stirred. Each wire was required to carry then only 
1 ampere, or develop only 4 watt-seconds heat energy. It was impossible to imagine 
that the temperature of the wire could have been sufficiently different to that of the 
oil to appreciably affect the resistance. A difference of ‘1° between the wire and oil 
