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24 of the Marquis of Worcester was revived twenty years later, by Sir Samuel Morland, but in what form is not now known.

In a memoir, which he wrote upon the subject in 1683, he exhibited a degree of familiarity with the properties of steam that could hardly have been expected of any one at that early date.

In his manuscript, now preserved in the Haarlem Collection of the British Museum, he states the size of the cylinders required in his machine to raise given quantities of water per hour, and gives very exactly the relative volumes of equal weights of water and of steam under atmospheric pressure.

He tells us that one of his engines, with a cylinder six feet in diameter and twelve feet long, was capable of raising 3,240 pounds of water through a height of six inches, 1,800 times an hour.

15. From this time forward the minds of many mechanicians were earnestly at work on this problem—the raising of water by aid of steam.

Hitherto, although many ingenious toys, embodying the principles of the steam-engine separately, and sometimes, to a certain extent, collectively, had beeu proposed and even occasionally constructed, the world was only just ready to profit by the labors of inventors in this direction.

But, at the end of the seventeenth century, English miners were beginning to find the greatest difficulty in clearing their shafts of the vast quantities of water which they were meeting at the considerable depths to which they had penetrated, and it had become a matter of vital importance to them to find a more powerful aid in that work than was then available.

They were, therefore, by their necessities, stimulated to watch for, and to be prepared promptly to take advantage of, such an invention when it should be offered them.

16. The experiments of Papin, and the practical application of known principles by Savery, placed the needed apparatus in their hands.

When Louis XIV. revoked the Edict of Nantes, by which Henry IV. had guaranteed protection to the Protestants of France, the terrible persecutions at once commenced by the papists drove from the kingdom some of its greatest men.

Among these was Denys Papin, a native of Blois, and a distinguished philosopher. He studied medicine at Paris, and, when expatriated, went to England, where he met the celebrated philosopher Boyle, who introduced him into the Royal Society, of which Papin became a member, and to whose "Transactions" he contributed several valuable papers.

He invented, in 1680, the "Digester," in which substances,