ox T?IE MECHANICAL EQUIVALENT OF HEAT. 
327 
The Dy-channels and Regulator admitting Cooled Water to the Bushes. 
26. Since the main supply must enter, as before, at the same pressure as the air 
within the vortices, while, in order to reverse the flow through the bushes, that 
entering the cap must enter at a little, but only a little, above that of the air within, 
while that entering’ on the brake side of the packing-ring in the stuffing-box must 
enter at any pressure up to 20 lbs., according to the load, above that of the air 
within, it was clear that there must be three supplies of water at different pres¬ 
sures under separate control; and it was equally clear that these supplies must all 
be at the same temperature. 
Fortunately, the arrangements already made for the new supply affbrded ready 
means of securing these conditions, as, in order to insure steadiness in the supply 
through the regulating valve, it had been provided, in arranging the pump, that there 
should be an excess of 20 lbs. on the square inch above that necessary to force the 
maximum water through the coil and to overcome the air pressure in the brake ; also, 
as the regulating cock was only a'l inch or two from the thermometer chamber, the 
water would be subject to little heating by radiation after leaving the cock, while 
the effect of radiation to the by-channels would be of secondary importance, as it is 
eliminated with the rest of the radiation in the difference of the trials. 
It thus became possible, by leading cooled water through two short by-branches, 
with separate regulators, from the supply pipe, before ])assing the main regulator, 
respectively into the aperture tlirough the stuffing-box on the inside of packing-ringj 
and into the cap on the inlet end, to secure controlled inflows of ice-cold water 
between each of the bushes and the shaft, and so to adjust the temperature of the 
bearing and insure lubrication of the shaft (tig. 9). 
In order to render such inflows steady and constant, it was desirable that the 
pressures before passing the regulator should be kept at a considerable and constant 
quantity above the vortex pressure in the brakes. 
From the first preliminary trials made with the branches it appeared that the 
turbine and pump were capable of supplying sufficient pressure for this, so that the 
only additions necessary were the branches. These were made of ^-inch brass pipe 
from the main pipe from the cooler as far as the branch regulators, and thence con¬ 
tinued by -g-inch indiarubber vacuum tube f inch outside wrapped with tape. The 
branch regulators have cocks, witli provision for fine adjustment, so that the vmry 
small quantities which passed might be definitely regulated to great nicety (Plate 5). 
With these it was found practical to maintain the temperature of the bushes from 
anything a few degrees above 32 to any required temperature. 
It is to be noticed that the work done by pressure over and above the pressure g>a 
in the inlet thermometer chamber is that due to the difference between the pressure 
in the main pipe before passing the regulators and pa, through whichever passage the 
water enters. And since in that water which passes into the thermometer chamber 
