156 
DR. H. T. BARNES ON THE CAPACITY FOR HEAT OF WATER 
replacing the water circulation by heavy lagging; its > effect can be measured by 
varying the flow of water, as will be shown further on. This conduction effect will 
be independent of the difference in temperature between the jacket water and the 
outside air, and depend on the rise of temperature (d, — d 0 ) directly, and on the 
velocity of flow inversely. 
Convection .—We have already discussed the effect of the stream-line flow on the 
radiation correction, when the water is not stirred in its passage through the flow-tube. 
It is proposed further on to treat this more in detail, as it has an important bearing 
on the general validity of this method applied to a non-conducting liquid. The effect 
of convection currents around the thermometer bulbs is avoided by suitably stirring 
the water. Strictly speaking, the thermal stream-lines in the flow-tube should not 
be classed as convection currents, but I have included them here for the sake of 
convenience. 
Gain of Heat .—The work done by the water in flowing through the fine tube may 
be measured by determining the difference in water-pressure between the inflow and 
outflow-tubes, for any given flow. The work done by any other flow can then be 
determined by measuring the change in temperature on the outflow-thermometer due 
to the change in flow. 
If W, be the work done by the flow Q x per second, 
’’2 j ) 5 > ) ■> Q$ i > 
then 
Wj = JQ X (6 1 — d 0 ) + (6 l — d 0 ) h and W 2 = JQ 3 (d 3 - d 0 ) + (d 2 - d 0 ) A, 
where d 0 is the temperature of the inflowing water as before, 
0 l and the temperatures of the outflowing water for the flows Q, and Q. : 
respectively, and 
h the heat-loss per degree rise, as before. 
Then W 1 - W a = J (Qj - Qo) (0 1 - d 2 ) + h (d! - do). 
But h is small, and (0 l — do) is small, so that we may neglect it in comparison to 
(Qi — Qo). If we find that (d x —- do) is negligible for a large value of (Q L — Qo), then 
we have W, = W 3 = 0. 
For the limits of flow and the size of flow-tubes I adopted in the present experi¬ 
ments, no measurable effect could be obtained on the outflow-thermometer. Even if 
the work done was appreciable, the method adopted of obtaining the “ cold ” readings 
for each flow would eliminate it, except if it varied with the change in the viscosity 
of the water, heated through the temperature (dj — d 0 ). 
Method of Measuring the Specific Heat .—"Referring to the original difference- 
equation, we see that 
4-2 Q (0 1 - d 0 ) 3 + (0 1 - d 0 ) h = EC - 4-2 Q (d x - d 0 ), 
in which there are the two terms 3 and h to be determined. If w r e take two flows of 
