"[T]o compare... the intensities of the constant flows of heat... propagated uniformly in the two solids, that is... the quantities of heat which, during unit of time, "cross unit of surface of each of these bodies. The ratio of these intensities is that of the two quotients \frac{a - b}{e} and \frac{a^\prime - b^\prime}{e^\prime}. ...[D]enoting the first flow by F and the second by F^\prime we... have \frac{F}{F^\prime} = \frac{a - b}{e}\div\frac{a^\prime - b^\prime}{e^\prime}."