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41.

(internal combustion) engine being about 40 per cent, and that for the best reciprocating steam engine but 21 per cent. This high efficiency is, of course, the result of three things; the absence of much heat loss due to the suddenness of the explosion; the almost entire absence of friction; and the high temperature of burning. Owing to these features, it is doubtful if even the most perfect turbine or reciprocating engine could compete successfully with the type of heat engine under consideration.

It is, however, the velocity ([[underlined]] c [[/underlined]] in equations (6) and (7)) which is of the most interest. The highest velocity obtained in the present experiments is 13 ft/sec under 8,000 ft/sec. thus exceeding a mile and a half per second (the "Parabolic velocity" at the surface of the moon), and also exceeding anything hitherto attained except with minute quantities of matter by means of electrical discharges in vacuum tubes. Inasmuch as the higher velocities range between seven and eight fold that of the Coston rocket we should expect a reduction of initial masses to be made possible by employment of the steel chamber, to at least the [[underlined]] seventh root [[/underlined]] of the masses necessary for a chamber like the Coston rocket.

The supposition is, of course, that the mass of propellant material can be made so large in comparison with the mass of the steel chamber, that the latter is comparatively negligible. No attempt was made in the present experiments to reduce the chamber to its minimum weight; in fact, the more massive it was, the more satisfactor^[[ily]] could the ballistic experiments be performed. The minimum weight was possible, for the same thickness of wall as in the experiments, was calculated by estimating, first, the volume of a chamber from which all superfluous metal had been removed, as shown by the