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17.

described must make an enormous reduction in initial mass as compared with that necessary for an ordinary rocket.

As a matter of possible interest, photographs were taken at night of the flash which accompanied the explosions produced by firing the small chamber.  These are given on the same sheet as Fig. 11, which shows the set-up for these experiments; the camera being in the same position as when the flashes were photographed.  The white marks, above the flash, are strips of cardboard, nailed to a long stick at intervals of 10 cm. and constituted a comparison scale, one end of which was directly above the "muzzle" of the gun.  This scale was illuminated, before the charge was fired, by a small electric flash lamp held in front of each strip for a moment; which lamp also illuminated a card bearing the number of the experiment.

The photographs bring out a curious fact; i.e., that the "flash" appears in most instances to be at a considerable distance in from of the nozzle.  This is easily understood if we admit that the velocity of the ejected gases is very high just as the gases pass out of the nozzle, but becomes very quickly reduced nearly to zero by the air.  In other words we may consider that the gases pass from the nozzle in an extremely short time -- far too short to affect the photographic plate; and that it is only when the velocity has been considerably reduced that the "flash" is photographed.

In experiment 11, a suggestion of this high-velocity portion of the flash is seen; which, it will be notice, is less in diameter than the end of the nozzle.  It should be remarked that it was only by accident that the nozzle was illuminated by the flashes in experiment 9 and 11 in such a was as to be seen in the photograph.