Regarding the recent Technical Note of Mr. RAsquith and Mr. Whitaker (May 1954 journal):1. The dependence of the weight of a given mass on location is a sufficient reason for the abolition of the ” weight” definition of specific impulse. This is likely to become increasingly apparent as rockets penetrate further into interplanetary space.2. It is convenient that the “weight” definition gives values of specific impulse which are independent of the units employed, provided that the units of thrust and weight are the same, for the unit of time employed in the definitions under discussion is the second. This raises the question of whether the unit of time should have been specified in the definitions. It seems to me that an improvement on fundamental grounds would be to define (S.I.)m as thrust per unit mass of propellants consumed per unit time and (S.I.)ω as thrust per unit weight of propellants consumed per unit time.