NO. 2 METHOD OF REACHING EXTREME ALTITUDES 35 



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 (internal combustion) engine being 

 about 40 per cent, and that for the best reciprocating steam engine 

 but 21 per cent. This high efficiency is, of course, the result of three 

 things : the absence of much heat loss due to' the suddenness of the 

 explosion ; the almost entire absence of friction ; and the high 

 temperature of burning. Owing to these features, it is doubtful if 

 even the most perfect turbine or reciprocating engine could compete 

 successfully with the type of heat engine under consideration. 



It is, however, the velocity (c in equations (6) and (/)) which is 

 of the most interest. The highest velocity obtained in the present 

 experiments is 13 ft./sec. under 8,000 ft./sec, thus exceeding a mile 

 and a half per second (the " Parabolic velocity " at the surface of the 

 moon), and also exceeding anything hitherto attained except with 

 minute quantities of matter by means of electrical discharges in 

 vacuum tubes. Inasmuch as the higher velocities range between 

 seven and eightfold that of the Coston rocket we should expect a 

 reduction of initial masses to be made possible by employment of the 

 steel chamber, to at least the seventh root of the masses necessary 

 for a chamber like the Coston rocket. 



The supposition is, of course, that the mass of propellant material 

 can be made so large in comparison with the mass of the steel 

 chamber, that the latter is comparatively negligible. No attempt was 

 made in the present experiments to reduce the chamber to its mini- 

 mum weight ; in fact, the more massive it was, the more satisfactory 

 could the ballistic experiments be performed. The minimum weight 

 possible, for the same thickness of wall as in the experiments, was 

 calculated by estimating, first, the volume of a chamber from which 

 all superfluous metal had been removed, as shown by the full lines 

 in figure 12, and then calculating the mass of this reduced chamber, 

 from the measured density of the steel. The minimum masses of 

 chamber per gram of powder plus wadding, estimated in this way, 

 were 143, 130, and 120 grams, respectively, for experiments 50, 51, 

 and 52. In the last tAvo cases, a smaller breech-block could doubt- 

 less have been used, as evident from figure 12 ; and in the first two 

 cases, the chamber wall, itself, could safely have been reduced in 

 thickness. More important still, a " built-up " construction would 

 much reduce the mass as has already been explained."^ 



