The quantity of heat so measured is the total heat of the vapour reckoned from the final temperature of the calorimeter, and the heat of the liquid h must be subtracted from the total heat measured to find the latent heat of the vapour at the given temperature.
This theory of the Leyden phial Franklin supported very ingeniously by showing that the outside and the inside coating possessed electricities of opposite sign, and that, in charging it, exactly as much electricity is added on one side as is subtracted from the other.
This supposes the present density nearly uniform; if it is not uniform, any amount added to the former period is subtracted from the latter.
At high speeds the centrifugal tension of the belt or rope, of amount wv 2 /g, may be considerable, and must be subtracted from the end tensions.
Numerical quantities, to be added or subtracted, must be in the same denomination; we cannot, for instance, add S5 shillings and loo pence, any more than we can add 3 yards and 2 metres.