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40.

curve concave to the axis of the nozzle.

[[underlined]] CONCLUSIONS FROM EXPERIMENTS [[/underlined]].

1. The experiments in air and [[underlined]] in vacuo [[/underlined]] prove what was suggested by the phographs of the flash in air, namely, that the phenomenon is really a jet of gas having an extremely high velocity, and is not merely an effect of reaction against the air.

2. The velocity attainable depends to a certain extent upon the manner of loading, upon the circumstances of ignition, and upon the form of the nozzle. Hence, in practice, care should be taken to design the cartridge and the nozzle for the density of air at which they are to be used, and to test them in an atmosphere of this particular density.

It is with pleasure that the writer acknowledges the use, as honorary fellow in physics, of the laboratory facilities, and especially the rotary pump, at the Physics Laboratory at Clark University where these experiments were performed.

[[underlined]] SIGNIFICANCE OF THE ABOVE EXPERIMENTS AS REGARDS CONSTRUCTING A PRACTICAL APPARATUS [[/underlined]].

It will be well to dwell at some length upon the significance of the above experiments. In the first place, the lifting power of both powders is remarkable. Experiment 51 shows, for example, that 42 lbs. can be raised 2 inches by the reaction from less than 0.018 lbs. of powder. One interesting result is the very high efficiency of the apparatus considered as a heat engine. It exceeds, by a wide margin, the highest efficiency for a heat engine so far attained -- the "net efficiency" or duty of the Diesel