NO. 2 METHOD OF REACHING EXTREME ALTITUDES I9 



without involving undue pressures ; and secondly, that large cham- 

 bers, even with comparatively short nozzles, are more efficient and 

 give higher velocities than small chambers. 



It is obvious that large grains of powder should be used in large 

 chambers if dangerous pressures are to be avoided. The bulging in 

 experiment 52 is to be explained by the grains of powder being too 

 small for a chamber of the size under consideration. It is possible, 

 however, that pressures even as great as that developed in experiment 

 52 could be employed in practice provided the chamber were of 

 " built-up " construction. A similar result might possibly be had 

 if several shots had been fired, of successively increasing amounts of 

 powder. The result of this would have been a hardening of the wall 

 of the chamber by stretching. Such a phenomenon was observed 

 with the soft steel chamber already described, which was distended 

 by the first few shots of Infallible powder, but thereafter remained 

 unchanged with loads as great as those first used." 



EXPERIMENTS IN VACUO 

 INTRODUCTORY 



Having obtained average velocities of ejection up to nearly 8,000 

 ft./sec. in air, it remained to determine to what extent these repre- 

 sented reaction against the air in the nozzle, or immediately beyond. 

 Although it might be supposed that the reaction due to the air is 

 small, from the fact that the air in the nozzle and immediately beyond 

 is of small mass, it is by no means self-evident that the reaction is 

 zero. For example, when dynamite, lying on an iron plate, is ex- 

 ploded, the particles which constituted thfe dynamite are moved very 

 rapidly upward, and the reaction to this motion bends the iron plate 

 downward ; but reaction of the said particles against the air as they 

 move upward may also play an important role in bending the iron. 

 The experiments now to be described were undertaken with the view 

 of finding to what extent, if any, the " velocity in air " was a fictitious 

 velocity. The experiments were performed with the smaller soft 

 tool steel and nickel-steel chambers that have already been described. 



METHOD OF SUPPORTING THE CHAMBER IN VACUO 



For the sake of convenience, the chamber, or gun, should evidently 

 be mounted in a vertical position, so that the expelled gases are shot 

 downward, and the chamber is moved upward by the reaction, either 

 being lifted bodily, or suspended by a spring and set in vibration. 



