Chapter VI
HOW AIR BALLOONS ARE MADE
IF you take an inflated bladder and immerse it in water and then let go of it, the bladder rises to the top and begins to float. In exactly the same way if you boil water in a kettle, you will see on the bottom, over the fire, how the water becomes volatile, becomes a gas; and when a little of this aqueous gas collects it immedi-ately rises to the top in the form of bubbles. First, one bubble flies up, then another, and when the water is thoroughly heated, then the bubbles rise unceasingly; then the water boils.
Just exactly as the bubbles filled with steam fly up to the top because they are lighter than water so up through the atmosphere will rise a balloon inflated with hydrogen gas or with heated air, because heated air is lighter than cold air, and hydrogen is the lightest of all gases.
Air balloons are made of hydrogen or of heated air. This is the way they are made of hydrogen. A large bag is made and attached by ropes to stakes, and then it is rilled with hydrogen gas. As soon as the ropes are cut, the balloon rises and floats until it escapes from the atmosphere that is heavier than hydrogen. But when it reaches a rarer Part of the atmosphere, the balloon stops rising and then it floats along like a bubble on the top of the water.
Balloons are made of heated air in this manner: a large empty bag is made with a wide mouth below like a pitcher upside down, and in the mouth is placed a bunch of cotton which is soaked with ether and then set on fire. The air in the balloon is heated by the fire and becomes lighter than the cold air outside, and the balloon rises like a bubble in water, and it floats up in the air until it reaches atmosphere so rare as to be lighter than the heated air.
Almost a century ago some Frenchmen the Mont-golfier brothers 1 invented the hot air balloon. They made a bag of cloth and paper and filled it with hot air; it floated. Then they made another still larger, attached a ram, a cock, and a duck to it and sent it up. The balloon ascended and returned successfully. Then they attached a small boat to it, and a man took his place in the boat. The balloon went up so high that it was lost to sight; it floated off and then came down without injury. Then they invented the method of inflating balloons with hydrogen, and they kept going higher and more rapidly.
In order to make a balloon ascension a basket is attached to the bag, and two, three, and even as many as eight men accommodate themselves in it, taking with them food and drink.
In order to regulate the movements of the balloon up and down at will, a valve is constructed in the balloon, and the aeronaut 2 can open it or shut it at his own pleasure. If the balloon rises too high, and the aeronaut wishes to descend, he opens the valve, the gas escapes, the balloon contracts, and begins to sink. Moreover, he always carries bags of sand. If a bag is thrown out, the balloon becomes lighter, and it rises. If the aero-naut wishes to come down, and sees that it is not a fit place for landing, on account of a river or a forest, then he empties out some sand, and the balloon becomes lighter and rises again.
Chapter VII
GALVANISM
ONCE there was a learned Italian named Galvani. He had an electrical machine and he was showing his pupils what electricity was. He rubbed glass vigorously with oiled silk, and then he approached to the glass a copper knob with a glass handle, and instantly a spark leaped from the glass to the copper knob. He told them that a similar spark would be elicited by sealing-wax and am-ber. He showed how feathers and pieces of paper are sometimes attracted by electricity, sometimes repelled, and why this is. He performed many different experi-ments with electricity and showed them to his pupils.
Once it happened that his wife was taken ill. He summoned the doctor and asked him how to cure her. The doctor ordered him to have made for her a frog soup. Galvani sent out to get some edible frogs. They were caught, killed, and laid on the table.
The cook did not come to get the frogs, and Galvani went on to show his pupils his experiment with the electrical machine, and produced sparks.
Suddenly he noticed that the dead frogs lying on the table moved their legs. He began to study them and discovered that each time he elicited a spark from the electrical machine the frogs kicked.
Galvani procured some more frogs and began a series of experiments. Each time it proved that whenever he produced a spark the dead frogs acted as if they were alive. And so it occurred to Galvani that living frogs might move their legs from this cause, that electricity might pass through them.
But Galvani knew that electricity is in the atmos-phere; that while it is more noticeable in sealing-wax, amber, and glass, still it is in the air, and that thunder and lightning are produced by atmospheric electricity.
So he began to make experiments whether dead frogs would move their legs ‘under the influence of atmospheric electricity. For this purpose he took some frogs, skinned them, cut off their heads and fore paws, and attached them by copper hooks to the roof, under an iron gutter. He thought that if a thunder-shower came up and the atmosphere was full of electricity, then the electricity would be brought to the frogs through the copper wire, and they would begin to kick.
But though several thunder-showers came up, the frogs did not move. Galvani proceeded to take them down, and while he was doing so, he touched the leg of one of the frogs to the gutter and the leg kicked ! Galvani then took the frogs and began to make the following experi-ment : he attached iron wire to the copper hook and then touched the frog’s leg with the wire the leg kicked.
Here Galvani came to the conclusion that all animals are alive only because they have electricity in them, and that electricity leaps from the brain into the flesh and thus animals move.
No one had at that time gone very thoroughly into the study of this matter, and as nothing was known about it, every one put faith in Galvani’s explanation.
But about this time another scientist, Volta, began to experiment for himself, and proved conclusively that Galvani was mistaken. He tried touching the frogs, not as Galvani had done with a copper hook and an iron wire, but first with a copper hook and a copper wire and then with an iron hook and an iron wire and the frogs did not stir. They moved only when Volta touched them with an iron wire attached to copper.
So Volta came to the conclusion that the electricity was not in the dead frog, but in the iron and copper. He continued to make his tests, and this was the result : As soon as he placed iron and copper together, electri-city was produced, and the electricity caused the dead frogs to kick. Then Volta began to try how to make electricity in a different way from what had been done before. He tried putting together various metals like the iron and copper, and he reached the conclusion that only from the contact of such metals as silver, platinum, zinc, tin, iron, he could produce electric sparks.
After Volta, new methods were invented for getting a stronger current of electricity by putting the metals into various liquids, water, and acids. By the use of these liquids electricity acquired so much more energy that it was no longer necessary to rub, as had been done be-fore; all that was required was to place in a single dish pieces of different metals and pour on them the liquid, and electricity would be created and sparks would be elicited.
As soon as this kind of electricity was discovered, methods were invented for putting it to use; they could cover objects with gold and silver by means of electricity, and by means of electricity they could transmit signals from one distant place to another.
To do this, pieces of different metals are placed in glass jars, and liquids are poured over them. The electricity is produced in these jars, and this electricity is conveyed by means of a wire to any desired place, and from that place is led into the earth. The electricity in the earth runs back again to the jars and is conducted into them by means of another wire. Thus this elec-tricity keeps going in a circuit, as in a ring by the wire to the earth and back by the earth and again by the wire and again by the earth. Electricity can go in either direction, according as you may wish : it may go first by the wire and return by the earth, or go first by the earth and return by the wire.
Over the wire, in the place where the signals are given, is placed a mag-netic needle, and this needle points in one direction if the electric current comes by the wire and returns by the earth, and in the other if the electric current comes by the
