NO. 2 METHOD OF REACHING EXTREME ALTITUDES 29 



SPRING IMPULSE-METER 



A section of the spring' impulse-meter is shown in figure 5(c). 

 The apparatus consisted of an aluminium disk, D, cemented to a lead 

 rod, L, of combined mass 5.295 gms. supported by a fine brass 

 spiral spring, S. The disk, D, was of a size sufficient to slide easily 

 in a glass tube, G. The upper end of the spring protruded through 

 a small hole in the glass tube, and was fastened at this point by 

 de Khotinsky cement, it thus being easy to make the top of the lead 

 rod level with the zero of a paper scale, K, pasted to the outside oi 

 the glass tube. A piece of white paper placed behind the tube, G, 

 made the motion of the lead rod L very clearly discernible. 



This impulse-meter was placed in a hole in the upper cap of the 

 12-inch pipe of the cylindrical tank, at D, figure 4, and plate 8, 

 figure I, the same distance from the wall of the 12-inch pipe as the 

 center of the 3-inch pipe. It projected one inch through the 12-inch 

 cap which was practically the same as the distance the 3-inch pipe 

 projected. The tube, G, was kept in position in the cap by being 

 wrapped tightly with insulating tape, the joint being finally painted 

 with the wax already described. 



The theory of the spring impulse-meter is given in Appendix D, 

 page 62, where O is the ratio already defined in connection with the 

 direct-lift impulse-meter. There are two reasons why the ratio, Q, 

 obtained in the Appendix should be larger than the true percentage 

 at the top of the 3-inch pipe. In the first place, friction in the 3-inch 

 pipe will decrease the velocity of the rebounding gas ; and, further, 

 the disk, D, figure 5, is fairly tight-fitting in the glass tube. G, 

 whereas there is a considerable space between the gun and the 3-inch 

 pipe, through which the gas may pass and, accumulating above, exert 

 a downward pressure on the top of the gun. 



One important advantage of the spring impulse-meter over that 

 employing direct lift is that the former has very little friction, so that 

 the readings are very reliable. Another advantage is that the dis- 

 placement of the former will include without any uncertainty the 

 effect of any number of rebounds following one another in rapid 

 succession^ — i. c, the effect o'f multiple reflections of the gas, if such 

 reflections are present. 



EXPLANATION OF TABLE III 



In the vacuum experiments, the soft steel chamber was used for 

 Du Pont powder, and the nickel steel chamber for Infallible powder. 



The three nozzles called short, medium, and long, were respectively, 

 9.64, 15.88, and 22.08 cm. from the throat to the muzzle. 



3 



