Coming back to our rocket: we certainly would feel that a rocket that was sent off in its flight by a maintained exertion of 20 horse-power would be a pretty big one. But,’once it had attained its desired velocity and was in outer space, the strain that drags upon its power, a resistance produced by the presence of air would almost entirely cease, the horse-power could be reduced to almost nothing, and the least little evolution of gas through a nozzle— rocket fashion—would suffice to keep it in motion at high Velocity. The whole problem, from a point of view of application of forcé and of the effect of change of motion upon the human system resolves itself into this same problem of acceleration.
The personal element comes into very definite consideration. If the traveler were enclosed in a protecting cabin, high speed would not affect him. But acceleration will, and it must be limited or the results will be disastrous to the inmates of the vehicle The chief medical examiner of pilots for the French air service is cited as statmg specifically that it is acceleration not speed that is dangeious to air travelers. Too quick starting may mean death. Ihe action of change of velocity upon the blood displaces it throwing the circulatory system into disorder and forcing thé blood into wrong distribution.
A speed of seventy miles an hour has been attained in one second of acceleration without injury, but it is believed that three or four times this rate would be injurious. The danger is empha-sized by the fact that the pilot should be in perfect physical condition.
Duration of acceleration has a specific effect. If prolonged beyond three or four seconds, discomfort is liable to ensue which is the warning of real trouble. ’
Another curious feature of high-speed traveling at a uni from rate is that a sudden turn, generating what is called centrifugal force, ^produces an effect similar to that of acceleration. The blood is driven violently to one side or the other or in one or the other direction and blood vessels may be ruptured.
It is easy to believe that, with a highly responsive airplane under him, a pilot may be tempted to develop a high degree of acceleration. In the dirigible this is not so easy. By the use of some adequate material for the lining of the balloonets, the leakage is controlled. Goldbeater’s skin was found to be an excellent material for the lining of the gas bags, but it seemed strange to go to nature for such material. Now efforts are being made to substitute some artificial substance for the lining for the gas bags of a balloon, instead of part of an ox’s intestines. It is probable that very soon the artificial product will be developed. When this is brought about, the dirigible, which at least insures against too high acceleration, may begin to come into its own.