Through the Earth/Chapter XXIX
A WEIGHTY SUBJECT
HERE was but one hope left, and this was that the telemeter might be wrong. But of this there was very little chance, as Dr. Giles had taken the greatest precautions to secure instruments that would be perfectly accurate. In fact, as it turned out in the sequel, the telemeter was correct to within a very small fraction of an inch.
But William did not know this at the time, and, in his anxiety to learn the truth at all costs, he glanced around at the different instruments in the car, and his attention was attracted to the spring balance already mentioned. To his surprise, the pound weight now exerted such a pull that the needle pointed to two ounces.
"What!" exclaimed William, in great astonishment. "Is it possible that objects in the car are really regaining their weight! At the start the needle of this balance pointed to zero; the last time I looked at it, it pointed to only half an ounce; while now it shows two ounces. If this balance is correct, and one pound weighs two ounces, then every object in the car must have regained one eighth of its full weight, and I myself must now weigh twelve and one half pounds."
A careful watch on the instrument showed William that his surmise was correct; for the needle of the balance gradually turned more and more, showing that the heaviness of objects in the car was increasing every second.
Our hero was at first unable to account for this strange fact. The whole journey had been a perpetual succession of surprises, but here was one that seemed to promise more interest than anything which had yet transpired.
His astonishment will be readily understood. He was sufficiently well versed in physics to know that a body at rest near the center of the earth would have little or no weight. Consequently, even if the car were standing still, at the point which he had reached the objects it contained should have almost no weight. On the other hand, since the car was falling in obedience to the attraction of gravitation, as all the objects in the car were falling with precisely the same speed, they ought to weigh absolutely nothing during any part of the journey!
But it was now plainly manifest that bodies in the car did have weight, a weight equal to one eighth of what they possessed upon the earth, and this weight was steadily increasing every minute!
Here was indeed a puzzle. William that morning was firmly convinced that during his fall through the earth all bodies in the car would at the start have their normal weight, but that at the center of the earth none of them would weigh anything at all.
Yet, in practice, what had occurred? The very reverse of what he had imagined. At the start, none of the bodies in the car possessed any weight, while here, as he approached the center of the earth, they were in some mysterious manner rapidly regaining their heaviness.
Then he remembered the doctor's words, and the explanation came back to him like a flash. Evidently this resumption of weight was due to the presence of air in the tunnel. The doctor had not been able to remove all the air from the tube, and what little was left sufficed to retard the car somewhat; and the greater the speed of the car, the more was it retarded by the resistance of the air.
"Ah, now I begin to understand," said William, thoughtfully. "The reason I had no weight before was because I fell just as fast as the car did, and so could never catch up with the bottom. But now that the speed of the car is checked by the resistance of the air in the tube, the bottom of the car is held back three or four feet every second; and as I am, of course, not held back at all, save by the trifling resistance of the air in the car, I am each second forced three or four feet nearer the bottom. And the faster we go, the more will the car be retarded, and the more I shall, consequently, weigh. As soon as the resistance is sufficient to retard the car thirty-two feet each second, I shall weigh just as much as I did upon the earth, namely, one hundred pounds. If the resistance becomes still greater, I shall weigh even more. When I reach the center of the earth, it is quite possible, as the resistance increases with the square of the velocity, that I may be falling at a sufficient speed for the car to be retarded one hundred and twenty-eight feet each second, in which case I should weigh four hundred pounds!
"Four hundred pounds! Just to think of it! I should be such a heavy, lead-like mass I could not stand upright, and would have the greatest difficulty even to drag myself around. I could scarcely move my hands or feet. Truly, I am in a veritable fairyland, and everything turns out just the opposite of what I expect. I would have sworn, this morning, that when the car started I should have my usual weight, and when it reached the center of the earth I should float around like a feather, without any weight. How has it turned out! Just the reverse! At the start I floated around like a feather, while at the center, far from floating around, I shall be an inert, lead-like lump, so heavy I can hardly move myself about! Surely, wonders will never cease!"