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39.

It now becomes possible to find, from the experimental results, the highest velocity [[underlined]] in vacuo [[/underlined]] upon which dependence may be placed. This is evidently the result of experiment 45 and is 2.34 km/sec. or 7,680 ft/sec. It is well worth noticing, however, that experiment 50 would have given, without doubt, a velocity even higher, had friction properly been taken into account.

[[underlined]] DISCUSSION OF POSSIBLE EXPLANATIONS. [[/underlined]]

1. The fact that the velocities are high in [[underlined]] vacuo [[/underlined]] than in air seems explicable only by there being conditions of ignition different in vacuo from those in air; although this may also have been due to the air in the nozzle interfering with the stream-lines of the gas, thus producing a jet not strictly unidirectional. It should be ^[[r]]emarked that the highest velocity [[underlined]] in vacuo [[/underlined]] recorded, experiment 25, may have been due to accidentally good circumstances of ignition; but may also have been due, in part, to being performed in the circular tank.

2. The fact that the medium nozzle gives in general velocities higher than the long nozzle shows that very likely after traveling the distance from the throat equal approximately to the length of the medium nozzle, the gas is moving so rapidly that it fails to expand fast enough to fill the cross-section of the nozzle. A discontinuity in flow is produced at the place where the gas leaves the wall of the nozzle, and this produces eddying and a consequent loss of [[underlined]] unidirectional velocity [[/underlined]]. The efficiency could doubtless be increased by constructing the nozzle in the form of a straight portion, corresponding to a cone of 8º taper, for the length of the medium nozzle; with the section beyond this point in the form of a