In the notation of the calculus the relations become - dH/dp (0 const) = odv /do (p const) (4) dH/dv (0 const) =odp/do (v const) The negative sign is prefixed to dH/dp because absorption of heat +dH corresponds to diminution of pressure - dp. The utility of these relations results from the circumstance that the pressure and expansion co efficients are familiar and easily measured, whereas the latent heat of expansion is difficult to determine.
One geometrical interpretation of the negative sign of algebra was early seen to be mere reversal of direction along a line.
The value of l may be easily shown to be (r i -Er 2)1r/2 (r i t r 2)a-+-c cos a, where the positive sign is to be taken for a crossed belt and the negative sign for an open belt.
