Abstract: The method of the computation of the upper-air tendency field due to Rossby1 and Miller and Thompson2 is marred by their arbitrarily cutting off of some terms which appear to be of the same order of magnitude but of the opposite sign.It is difficult,or practically impossible,to justify their method theoretically.In this paper,instead of using the equation of continuity as they have done,we employ the advective conservation of temperature for the derivation of the upper-air tendency field.It is ismilar but with some corrections.It is proposed that this formula (10),instead of their original formula,may be used with advantage for the work.