If this vanishes for all values of X, u, v, ~, s~, ~ we must have X, Y, Z, L, M, N = o, which are the conditions of equilibrium.
If all the water be frozen, we have the vapour pressure curve of ice OB; while, if the pressure be raised, so that all the vapour vanishes, we get the curve OC of equilibrium between the pressure and the freezing point of water.
We find Prester John in one more phase before he vanishes from Asiatic history, real or mythical.
About the vertical; this vanishes if ~ FIG.
If at any instant the direction of one of the crank-arms coincides with the line of connection, the common perpendicular of the line sf connection and the axis of that crank-arm vanishes, and the 3irectional relation of the motions becomes indeterminate.