THE LAW OF RESISTANCE IN PARALLEL CHANNELS. 
953 
themselves—the temperature of the tank was 11° C. above that of the room, and 
the cooling arising from the top and sides of the tank must cause circulation in the 
tank. A few streaks of colour added to the water soon showed that such a circu¬ 
lation existed, although it was very slow. Another source of possible disturbance 
was the difference in the temperature at the top and bottom of the tank, this had 
been as much as 5°. 
In order to get rid of these sources of disturbance it was necessary to have the 
tank at the same temperature as the room, about 54° or 55°. Then it was found by 
several trials that the eddies came on at a fall of about I inch in 64 seconds, which, 
taking the viscosity into account, was higher than in the previous case, and this was 
taken to indicate that there was less disturbance in the water. 
As it was difficult to alter the temperatures of the building so as to obtain 
experiments under like conditions at a higher temperature, and it appeared that the 
same object would be accomplished by cooling the water to its maximum density, 40°, 
this plan was adopted and answered well, ice being used to cool the water. 
Experiments were then made with three tubes 1, 2, 3, at temperatures of about 
51° and 40°. All are given in Table I. 
