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 will then fall in the tube, till it gets to that
height which the atmosphere will sustain. This is nothing more than the
barometer used in all our houses. If the action of the tube be equal to
a square inch, the weight of the column of mercury in the tube would be
exactly equal to the weight of the atmosphere on each square inch of
surface. Thus Papin discovered a great step in the steam-engine, though
it was not much acted on for some years; he was also the first who
proposed to drive ships with paddles worked by steam.