The Cornish engines have been alluded to in connection with the Newcomen engine. Probably no large pumping engines in the past have held, and deservedly so, as high repute as have the Cornish engines when used for deep mine pumping. Their construction, with the rude appliances at hand, is not only a marvel but as well a high tribute to the ingenuity of those who designed them and to the skill of the workmen who built them. A rather full illustrated description of this almost unexcelled machine will be found later on in the book. _The next class of large steam pumping-engines which have played an important part in the history of hydraulic engineering may be grouped together as “rotative engines.”_ What is here meant by the term “rotative” is engines in which there are parts which make complete and continuous rotary motion and in which are used, in some way or another, shafts, cranks and fly-wheels. These engines vary greatly in their design and in the details of their construction. They are of varying sizes, including some of the largest and most expensive in the world. As a general thing they are employed in supplying towns and cities with water, and in some cases freeing shallow mines of water. The application of the power of the steam used in the steam cylinders in this class of engines to drive the plungers or pistons in the pumps, varies greatly, both as to the general design upon which they are built, and in the detail of their construction. In some instances it is through the use of long or short beams or bell cranks, sometimes through gearing, and occasionally through the plunger or piston of the pump direct; but in all cases the limit of the stroke of the steam piston, and of the pump plunger, is governed by a crank on a revolving shaft. Attached to the revolving shaft is _a fly-wheel_ of greater or less diameter and weight, which, in addition to assisting the crank to pass the center at each end of its stroke, _is employed to store up at the beginning of each stroke of the steam piston, whatever excess of power or impulse there may be imparted to it, beyond that required to steadily move the water column, and to give out again, toward the latter part of the stroke, when the power of the steam is of itself below that required to move the water column, the power previously stored in it_. In this respect the function of a revolving fly-wheel on a rotative engine is the same as is the weighted plunger in the Cornish engine; both being used for the purpose of permitting the steam to be cut off at a portion of its stroke in the steam cylinder, and expanded during the rest of the stroke. In short, these devices, as employed in both the classes of pumping engines described, were used in order that the best economy in the consumption of steam by means of early cutoff and a high grade of expansion, might be attained. The succeeding class of pumps to be described, driven by steam are _direct acting steam-pumps_.