CHAPTER VIII. The Inventor of the Steam-Engine

THE INVENTOR OF THE STEAM-ENGINE

IT has long been supposed that the steam-engine was invented by an Englishman of the name of James Watt. But the real inventor of the steam-engine was Denis Papin, a French doctor, who invented the engine while in Germany, and described it in a book which he published in England, where he lived for many years. He made friends with Huygens in Paris, and assisted him in carrying out his experiments on the air-pump.

Huygens was very busy with a great variety of inventions, and was glad to have this young assistant, who would carry out experiments for which he himself had no time.

Papin made a number of improvements in the air-pump. One of these was a cock, constructed on the principle of a gas cock or water tap, but having two channels through it. Another great improvement which he made in the air-pump was that he put the objects under a glass shade instead of in a bottle. The shade was placed upon a flat plate, and its edge was well greased, so that no air could enter from below.

In the middle of the plate was a hole, and the air was pumped out from below through this hole. Air-pump experiments could thus be made with a great number of different objects, one after the other, by simply lifting off the shade and replacing it after putting the object upon the plate. This method was easier than screwing off the cap of the bottle used by Huygens.

Papin described these improvements in the year 1674 in a little book called Experiments on Empty Space, with a Description of the Machines by which it is obtained. The little book was dedicated to his master Huygens, to whom he wrote as follows:--“These experiments belong to you. I have made nearly all of them according to your instructions. But I know that they are only a recreation to you. You would never have written them down, and certainly you would never have published them. And so, I am sure, you will not mind my doing it for you.” Ten years after his book was published, Papin was appointed by the Royal Society of London a curator of experiments, his duty being to devise and show experiments to the members of the Society.

Papin was greatly interested in mining, and he was always puzzling about some way of pumping up the water out of a mine. At that time the pumping had all to be done by hand, and it was done by a string of buckets, such as are used in wells. Papin had the idea of making a water-mill--driven by a brook—pump the water out of the mine. But this method was difficult unless a brook was close to the mine. However, Papin designed a system by which the water-power could be transported easily to the shaft of the mine. The water-mill drove the pistons in two cylinders connected with a long pipe. The pistons compressed the air and drove it along the pipe till it got to the mine.

At the mine there was a big wheel, or pulley, bearing a rope with buckets attached to it. Other ropes were attached to the shaft of the pulley, and were fixed to two other pistons moving in two cylinders. These cylinders were connected with the pipe containing the compressed air. First one cylinder was connected, and the buckets were lowered; then a tap was turned which connected the other cylinder instead, and this raised the buckets full of water.

This plan was a great improvement on the hand-pump (p. 70), but it was not quite satisfactory; and it failed when the brook ran dry in summer or was frozen in winter. Also the pump was rather a clumsy one. Papin invented a better instrument, which he called the centrifugal pump, and it is used to the present day. The pump consisted of a round, flat box containing a paddle wheel which whirled the water round. The water entered the box at the centre of the paddle-wheel, and on one side of the box was a pipe through which the water escaped on being whirled round. Papin tried to use this pump for pumping water, but he found that he had no machine for moving it quickly enough, nor did he get such a machine until he had invented the steam-engine. This, however, he did not succeed in doing for many years, and meanwhile he invented a number of other instruments.

One of these was a submarine boat. The first man to invent a diving-bell which could move under water was named Drebbel. He was said to have taken a trip under the Thames, disappearing entirely under water and coming up in a distant place. Some years after this, Boyle asked a medical doctor who had married a daughter of Drebbel, how it was that Drebbel and his crew were not suffocated under the water. He was told that Drebbel possessed a certain extract of air which enabled him to breathe in a confined space. We are nowadays not able to tell how much truth there was in the story concerning Drebbel.

But it is certain that Papin succeeded in constructing a diving-bell, and in using it under water. His diving-bell was not a bell at all, but a round box 6½ feet high, in which three men could stand upright. When sunk under water it did not disappear entirely, because a pipe stuck out of the top through which fresh air could enter or the used-up air be pumped out. The pump which did this was one of Papin’s own centrifugal pumps. On one side of the diving-bell was a very wide tube, through which a man could crawl. It had a little door at the extreme end which could be opened under water. This would, of course, let in the water, but Papin, with one of his pumps, drove air through the tube from within the diving-bell. This stream of air kept the water back, and the poor man in the tube (he must have been very uncomfortable) could do some work in the water outside, such as laying a mine for exploding an enemy’s ship.

Few people know that Papin was the real inventor of the steam-engine. But everybody acknowledges his invention of a kettle for cooking food under high pressure. He called it a “digester.” When water is boiling it cannot be made any hotter by putting greater heat under it. Greater heat simply makes it boil away more quickly. But it can be made hotter by preventing the steam from escaping. When the lid is stuck on tight, and the spout is stopped up, the steam cannot escape until it reaches a high pressure, and this means a higher temperature at which the water boils.

Papin, therefore, constructed a kettle which was closed at the top by means of a heavy weight. He did not close up the kettle with a screw, since that would have led to an explosion. He only made sure that the steam could not escape until it was hot enough and strong enough to lift the heavy weight. People thought at that time that if they could cook things at a very high temperature, they could get nourishment not only out of meat, but out of the bones as well. They thought they could make the bones eatable. Papin thought so too, and he cooked some bones in his new kettle. The hardest bones of beef and mutton were made as soft as cheese, and the extract from them made thick jelly, though the bones themselves were not good to eat. The digester is used to obtain gelatine from bones in this way at the present time.

When Papin seriously set about inventing the steam-engine, he was guided by what he remembered about a machine invented by Huygens. In the year 1674 he had himself constructed this machine. It was intended to raise water by an explosion of powder. The water was intended to be used for the great water-works in the palace of the King of France. A long cylinder containing a heavy piston was fixed in an upright position. In the bottom of the cylinder was a plug which could be screwed in. Before it was screwed in, some gunpowder and a slow match were placed on the plug. Shortly after the plug was screwed in, the match lighted the powder, the powder exploded, and drove the piston up to the top of the cylinder. When the cylinder cooled down, the pressure of the air drove down the piston. The piston was made to pull a chain going over a pulley to which buckets were attached.

In the year 1690, Papin took the first step towards constructing the steam-engine by inventing a cylinder in which the piston, instead of being driven by the explosion of gunpowder, was forced upwards by boiling some water under it. This plan made the plug unnecessary. The piston A was driven up by the steam, and fixed at the top by a rod E until it could be taken off the fire and made to do some work. There was one difficulty about this cylinder. If the piston fitted tight, it was not able to sink down to the level of the water at the bottom of the cylinder, because in doing so the air in the cylinder would be compressed, and would resist with a great force.

This difficulty was got rid of by Papin by means of another rod M, which fitted in a hole in the piston. This rod was pulled out so as to let the air escape. When the piston was down far enough, the rod was pushed into the hole again so as to stop it up.

The great fault of this machine was that the cylinder had first to be heated in order to drive out the piston and afterwards cooled, both of which processes took time. About the year 1704, a German prince gave Papin the order to build a steam-engine for pumping up water.

Just at about that time Papin had seen a design of a machine by a man of the name of Savery, which was not, however, a success. His own machine consisted of a boiler which was to be put in the fire and kept there. The steam from this boiler was conducted into a cylinder half-filled with water. On the top of this water there was a wooden float, so that the steam hardly came into contact with the water at all. The float contained an iron box, into which a red hot iron ball was placed. The steam, therefore, was not cooled on entering the cylinder, but drove the float to the bottom of the cylinder and forced the water into an upright pipe which was surrounded by another cylinder. This water compressed the air in the second cylinder, and valves were so arranged that the air could not turn back. It was therefore used for forcing water up a pipe. Water was then allowed to return into the first cylinder, and the operation was repeated. The first cylinder afterwards always remained sufficiently hot to preserve the power of the steam. In this respect Papin’s machine was a great improvement on Newcomen’s machine set up at Wolverhampton in the year 1711.

Papin tried his machine in the presence of the German prince in the year 1706. He did succeed in pumping water seventy feet high, but the long pipes began to leak, and the German prince was so disgusted that he would not give the money necessary to carry out any further experiments. Papin, therefore, went back to London, and in the next year he published a book called New Art of Lifting Water with the Help of Fire in a most Successful Manner. He had great plans about his machine. It was not only to pump water out of mines, but also to fire guns, and to drive ships and carriages.

But Papin died a few years afterwards without being able to carry out his great ideas beyond constructing a paddle-boat. He was one of the world’s greatest inventors, but the engineers of his time were not able to carry out his great inventions. Though his engine differs very greatly from the steam-engines now made, it certainly contained a piston working in a cylinder, and a safety valve, which are essential parts of a modern steam-engine.