ON THE MECHANICAL EQUIVALENT OF HEAT. 
351 
The number of revolutions with the bushes closed, counting ordinary work as well 
as the trials, is found from the records to be less than 300 X 60 X 360, and the 
number of runs to be 80, the mean time being 4‘5 hours. The revolutions during 
any one of the accepted trials were 300 X 60. And the trials were made in threes, 
so that the coefficient for oxidation would be 
Hence, the metal w'orn by abrasion in a single trial would he less than sgoth of 
1 lb. = 0'0028 lb., and the metal oxidised in one trial less than -g-ioth = 0'004 lb. 
So far the estimate is fairly definite, but, in order for its completion, it is necessary 
to arrive at some conclusion as to the work absorbed in disintem’ating’ the metal, 
and of the heat developed by its oxidation. 
There does not seem to be any reason v.doy there should be mure oxidati'Ui of the 
bright surfaces in a light trial than in a heavy trial, so that there would have been 
no error from this cause in their difference. 
As regards the abrasion and the oxidation of the abraded metal, there would be a 
difference, as the weight on the shaft in a heavy trial is 1 23 of the weight in a light 
trial. Thus the differences of abrasion would have been 
0-0006 lb. 
The work necessary to produce a state of disintegration, such as exists in the 
vapour of the metal, would be the total heat of vaporization, less the kinetic energy 
and work — [/^i,/(T — 32) + TV], and, although the heat of vaporization of the 
metal is not known, it would seem that it cannot greatly exceed, when subject to the 
deductions mentioned, the heat of vaporization of ice subjected to like deductions 
(1,000,000 ft.-lbs.). 
Assuming this, since the difference in the work of two trials is about 
70,000,000 ft.-lbs., the correction would be 
- 0 - 00001 , 
which, considering that the disintegration would be very imperfect, may be taken as 
an outside limit, while the effect may have been even reversed by the oxidation of 
the degraded meral.—Nov. 9, 1897.] 
Accidents. 
55. In contemplating such an extensive and complex research, the result of which 
depends on the mean of a number of experiments, it was impossible to overlook the 
question as to how such accidents, as would probably occur, should be dealt with. 
It was clear that, whatever the rule might be, it must be definite and rigorously 
applied. 
Two other things were also clear, that, as in surveying, accidents might occur, say 
