THE LAW OF RESISTANCE IN PARALLEL CHANNELS 
963 
The discharge in cubic centimetres divided by the area of section in square milli¬ 
metres gave the mean velocity in metres per second as given in the Tables III., IV., 
and V. 
The logarithms of i and v are given for the sake of comparison. 
31. The temperature .—The chief reason why the water from the main had been 
used was from the necessity of having constant temperature throughout the experi¬ 
ments, and my previous experience of the great constancy of the temperature of the 
water in the mains, even over a period of some weeks. 
At the commencement of the experiments the temperature of the water when 
flowing freely was found to be 5 C. or 41° F., and it remained the same throughout 
the experiments. Nevertheless, a fact which had been overlooked caused the 
temperature in the pipes to vary somewhat and in a manner somewhat difficult to 
determine. 
This fact, which was not discovered until after the experiments had been reduced, 
was that the temperature of the workshop being above that of the main, the water 
would be warmed in flowing through the pipes to an extent depending on its flow. 
The possibility of this had not been altogether overlooked, and an early observation 
was made to see if any such warming occurred, but as it was found to be less than 
half a degree no further notice was taken until on reducing the results it was found 
that the velocities obtained with the very smallest discharges presented considerable 
discrepancies in various experiments ; this suggested the cause. 
The discrepancies were not serious if explained, so that all that was necessary was 
to carefully repeat the experiments at the lower velocities observing the temperatures 
of the effluent water. This was done, and further experiments were made (see 
Art. 33). 
