350 
PROFESSOR O. REYNOLDS AND MR. W. H. MOORBY 
The Worh done hy Gravity on the Water. 
53. The difference of pressure on the bulbs of the initial and final thermometers 
which are at the same level, expressed in feet of water, is the work done by gravity 
per lb. of water. If and_^92 express these pressures in inches of mercury, the work 
done by gravity is 
1T4 (pi — P 2 ), 
which gives as the relative correction for the ecpiivalent, approximately. 
+ 0-000008 S[W - 2?o)]/2(W). 
The Work ahsorhed in Wearing the Metal of the Bushes and Shaft. 
[ 54 . During the six years the brake had been in use, before the trial commenced, 
the shaft and bushes were occasionally lubricated with oil, chiefly to prevent oxida¬ 
tion of the shaft when standing, and, up to the commencement of the trials, there 
was hardly any appreciable sign of wear. After the closing of the bushes by the 
stuffing-box and cap, when the use of oil was purposely discontinued, there was no 
means of observing the w^ear of the metal as long as the brake w^orked satisfactorily, 
as it did during all the trials. But when, after the completion of the trials, the 
stuffing-box and cap were removed, in order to return to the original manner of 
working, the excess of leaking through the bushes showed that there had been con¬ 
siderable wear. 
At that time it did not occur to me that the proportion of this wear, which took 
place during the actual running of the trials, would represent a certain amount of 
work absorbed in disintegrating tlie metal, or a certain amount of heat developed bv 
the oxidation of the metal, and no attempt was then made to form a definite estimate 
of the amount of metal which had disappeared. ^As, however, the worn metal was 
replaced by a coating of white metal, the thickness of this (less than s^nd of an inch) 
and the extent ot surface (less than 124 square inches) subsequently sho'ved that it 
could not be more than 1 lb. 
This w^as after ft occurred to me that however small might be the effect of this 
wear, since it was definitely observed to have taken place during the twelve months 
when the bushes were closed for the purpose of the trials, it was desirable, in oi’der to 
complete the research, that some outside estimate should be obtained of the limits to 
its possible effect, whether from disintegration or from oxidation. 
In as far as the loss of metal was due to the abrasion of the clean metal surfaces, it 
would be proportional to the number of revolutions, while in as ffir as it was owing 
to the oxidation of the metal surfaces, left bright after each run, it would be probably 
proportional to the number of runs. 
