dinner was being prepared lifted up by the vapour of the water boiling inside.  Reflecting on this, he turned his mind to the matter, and thought that this vapour, if rightly applied, might be made a useful moving power.  He thus describes his invention in his 68th Article:  “I have contrived an admirable way to drive up water by fire, not by drawing or sucking it upwards, thirty-two feet.  But this way hath no bounds, if the vessels be strong enough.”  He then goes on to say, that “having a way to make his vessels, so that they are strengthened by the force within, I have seen the water run like a constant stream forty feet high.  One vessel rarified by fire driveth forty of cold water, and one being consumed, another begins to force, and refill with cold water, and so on successively, the fire being kept constant.  The engineman having only to turn two cocks, so as to connect the steam with the one or the other vessel.”

In this engine, if it can be called an engine, we see that the Marquis had a good idea of the power of steam, but he had none, you will observe, as to the action of the condensation which would immediately take place when the steam from the boiler was brought into contact with the cold water to be raised.  Therefore this plan would be most expensive, on account of the great loss of steam by condensation.  It was, however, quite able to produce the effect, though only equal to raising 20 cubic feet of water, or 1250 lbs., one foot high by one pound of coal, or about the two-hundredth part of the effect of a good steam-engine.  After this, of course, it proved of no avail; but still we may say that the Marquis of Worcester was among the first who tried to make, and did do so, steam a moving power.

Our next is Denys Papin (died 1710), a native of Blois, in France, who was mathematical professor at Marpurg.  To him is due the discovery of one of the qualities of steam—­its condensation, so as to produce a vacuum, to the proper management of which our modern engines owe much of their efficacy.  Papin seems to have been the first who conserved the idea of the cylinder and piston, which he made to act on atmospheric principles—­that is to say, he took a cylinder with a piston moving up and down in it, and found that by removing the air from under the piston in the cylinder, that the pressure of the atmosphere would drive it down to the bottom of the cylinder:  this he performed by admitting steam, and then condensing it rapidly, so causing the required vacuum.  The pressure of the atmosphere is as near as may be 16 lbs. on every square inch of surface on the globe:  this is obviously the weight of the columns of air extending from that square inch of surface upwards to the top of the atmosphere.  This force is thus measured:  Take a glass tube 32 inches long, open at one end and closed at the other; provide also a basin full of mercury; let the tube be filled with mercury and inverted into the basin.  The mercury