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.
A very curious point comes up in the discussion of interplanetary traveling, that is of traveling through the almost complete vacuum of space. This is the power which would be required to propel a space ship, as it were, through space, when away from and out of the atmosphere of the earth. High resistance would be encountered in getting away from the earth due to the air. As long as the space ship, as we may call it, would be in the lower atmosphere of the earth at 10 or IS pounds pressure to the square inch, a great resistance to its motion and to its acceleration would be imposed by the air.
The overcoming of this resistance is the principal work of the airplane’s or dirigible’s engines. But if the ship, started vertically, or approximately so, from the surface of the earth, twenty miles of travel would get it rid of a very great part of the earth’s atmosphere, and ten or fifteen miles more would virtually bring it into the vacuum of outer space. As soon as there would be no air to oppose its motion, very little power— hardly any, in fact—would be required to drive it ahead, without regard to its speed, provided this were constant. Acceleration and its rate would be resisted only by the mass of the body to be accelerated. This resistance is due to what is called “inertia.” Inertia, if we look up its etymological origin, may be translated as the “laziness of matter,” for even in real life, especially in humanity, laziness is sometimes the deadest kind of resistance. The logical way to treat the subject would be to start our vehicle at a reasonably low, slightly accelerating velocity and to impose the real vigorous acceleration only when the vacuum of outer space would be reached and there was no air to oppose its motion, and to reach this place need not take but a few minutes. Here is the place where the so-called “ratiocination” of the Goddard rocket comes in.
Out of the earth’s atmosphere, and with practically nothing to contend with but the inertia of the mass of the object being propelled—and this only when accelerating—it would be found on calculation that an astonishingly small power would be required to accelerate and virtually no power to keep in motion a body of any mass in space. In the physical sense, mass is a definite factor, and weight may be expressed as an accident. The mass of a body is a real thing; it is 1/32 part, approximately, of its weight. If the body were taken out into space far away from the earth, it would have no weight, but its mass would be unchanged. Mass divided by 2 and multiplied by the square of the velocity in feet per second gives us its inertia, its resistance to a cessation of motion. To impart a velocity of 100 feet per second to a three-ton object in space would require the exertion of about 1,000,000 foot-pounds.
The Lights in the Sky
We saw the lights our first evening out from New York. They grew in splendor until, for three of us, the voyage ended. For the others, they may still move sometimes in the sky. They have never been explained, not even by Pretloe, who found some reason for every other fantastic thing that happened.
Standing by the rail after dinner that first night, I watched them. The sea was a little rough, but most of our passengers were veterans. Nobody had retired except one old lady. We stood along the rail or walked about the deck, speaking to each other occasionally with that shyness peculiar to people who meet for the first time on board a ship—especially a small ship—the first day out. The man beside me was Pretloe, but I didn’t know that then.
“Curious,” he said. “They don’t look like an ordinary display.” I noted his soft, precise voice, and his traveler’s accent—that slightly foreign but indistinguishable trick of speech which marks a linguist. I said:
“I’ve never seen the aurora borealis. I don’t know why I haven’t.”
The story continues next time …