CH. XXVIII.

CONDENSATION OF STEAM.

249

ice, E. Now as long as the tap, c, is kept open, the steam which is constantly rising from the water in B will rush along the tube into the empty flask, A, and will there be turned into drops of water by the cold of the ice underneath, and this will go on as long as there is any water left in B, because there will always be an empty space or vacuum in a to receive the steam as it rises. When the tap, c, is shut, the steam in B will become very dense, and when it is opened

A, Flask empty of air. B, Flask half-full of water and empty of air. c, Tap connecting the two bottles. D, Spirit lamp keeping the water in в boiling. E, Basin of ice cooling down the steam which passes into A.

again the greater part of the steam will rush out and be cooled down in A, while B remains hot as before.

Watt's Engine.-This was exactly the plan Watt adopted in his steam-engine; в answers to his cylinder (Fig. 43), which could be kept always hot, and A to his condenser, in which his steam was turned back into water. We cannot follow out all the different steps of his invention, and must content ourselves with a rough description of his engine after he had completed it, as shown in Fig. 43.

In the first place you must notice that cold water is kept flowing down from the tank A into B, and out through the pipe C, so that the condenser standing inside в is kept quite cold:

and, secondly, I must tell you that the rods, I and 2, are so placed that when the engine-end of the lever-beam is raised, as in the figure, the stopcocks a and c are open, and b and a are shut; and when that end of the beam falls, b and d will be open, and a and c will be shut.

Let us now begin with the machine as we see it in the figure. In this position of the beam the cocks a and c are open; therefore, the steam below the piston will rush out at

A, B, Cold water tanks. c, Outlet for cold water. D, E, Pumps for drawing off hot water and sending it along s, s, back to the boiler. P, Tight-fitting piston. a, d, Cocks for letting steam into the cylinder. b, c, Cocks for letting steam out of the cylinder. e, e, Pipe which carries steam from boiler to cylinder. o, o, Pipe which carries steam from cylinder to condenser. 1, 2, Rods connecting the cocks with the lever-beam.

c into the condenser, there to be turned into drops of water, while the steam from the boiler, entering at a, will force the

CH. XXVIII.

WATT'S ENGINE.

251

piston down. But now, the piston having pulled down the beam, a and c will be closed and the other two cocks, b and d, will be opened. So the steam above the piston will rush out at b into the condenser, while the steam from the boiler will pass directly from e down to d, and coming in below the piston, will drive it up again. In this way, although the cylinder is never cooled, the piston moves steadily up and down; because the steam is driven off into the condenser standing in B, where it is turned into water, and is drawn up by the two pumps D and E, and sent along the pipe, s, s, back to the boiler.

This was the principle of Watt's double-acting steamengine, and if you understand the difference between Figs. 41 and 43 you will see that, though Watt was not the first to make engines move by steam, he was the first to make a pure steam-engine, where the piston moves up and down without any help from the outside air, or of the counterbalancing weight e, Fig. 41, and without the enormous waste of heat and fuel which made all the earlier engines comparatively useless.

I have only told you here of the way in which he applied steam to his engines; all the numberless other improvements which he made you must read about in books on engineering. For twenty long years he went on improving and inventing without reaping any reward for his labour. Other men tried to steal his ideas and to make a profit out of his genius, and he had to fight against prejudice and injustice, and against constant depression caused by his own ill-health. Yet he found many kind friends upon his road, and amongst the most famous of these was Boulton, the Birmingham manufacturer, who became his partner in 1769, and stood by him manfully in all his difficulties and troubles. It was from

Boulton's manufactory at Soho (a suburb of Birmingham) that Watt's engines went forth to the world, and worked that great change in the manufactures of England which has made us one of the first nations of the world.

The names of Boulton and Watt deserve to be classed together as benefactors of mankind. Watt was the inventor, the man who loved science, and who could not live without creating. Boulton was the large-minded, enterprising man of business; he gave Watt men, money, courage, and support to carry out his inventions; and by his sympathy with, and command over the workmen, he led the army which conquered indifference, persecution, and difficulties, and established steam machinery in all the workshops of the world. Watt died in 1819, in the eighty-third year of his age, and was buried in Handsworth Church, near his friend and partner Boulton, who had died ten years before.

Chief Works consulted.-Black's 'Elements of Chemistry,' 1803; Edinburgh Review,' vol. xiii. 'History of Steam-engines;' Arago, 'Biographies of Scientific Men,' 1857; Smiles's 'Lives of Boulton and Watt;' Everett Deschanel's 'Natural Philosophy;' Tyndall's Natural Philosophy;' Balfour Stewart's Treatise on Heat ;' Beckman's 'History of Inventions.'

CH. XXIX.

BENJAMIN FRANKLIN.

253

CHAPTER XXIX.

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). Benjamin Franklin, born 1706—His Early Life -Du Faye discovers two kinds of Electricity-Franklin proves that Electricity exists in all bodies, and is only developed by Friction-Positive and Negative Electricity-Franklin draws down Electricity from the Sky -Invents Lightning-conductors-Discovery of Animal Electricity by Galvani-Controversy between Galvani and Volta-Volta proves that Electricity can be produced by the Contact of two Metals-Electrical Batteries-The Crown of Cups-The Voltaic

Pile.

Benjamin Franklin, born 1706.-He Investigates the Nature of Electricity, 1746.-Benjamin Franklin, the printer and man of science, was born at Boston, in America, in the year 1706. He was the son of a tallow-chandler, and had so many hard struggles in his early life that he does not seem to have turned his thoughts to science till he was nearly forty years of age. His father intended him for the Church, but there was not enough money to pay for his education, so he was apprenticed to his brother, who was a printer. Here he worked very hard, yet he used to snatch every spare moment to read any books which came within his reach; but his brother being unkind and harsh to him, a quarrel sprang up between them, and Benjamin at last ran away to New York, and from there to Philadelphia. In this last place he got a little work, but hoping to do better in England he came to London, where he learnt many of the