Such an outfit can be hauled to any point in the mine and there operated from some convenient circuit such, for instance, as the circuit supplying power to mine locomotives. [Illustration: FIG. 244.] The pump and motor shown in Fig. 244 are mounted on an iron truck, no wood whatever being used in construction, so that adjustment cannot be affected by moisture and an easy running and durable pump is assured. The pumps are made as compact and strong as possible for mine service, which is usually exceptionally rough and continuous. They are of the horizontal type which is best adapted for low passageways and are designed so as to afford easy access to all parts. The pumps are single acting and the plungers are provided with outside stuffing-boxes, which can be packed, and being in sight, any leakage can be quickly detected. Access to all valves is made easy by the removal of one large hand-hole cover on the valve chest. THE STEAM PUMP [Illustration: FIG. 245. G. KIRKHAM] THE STEAM PUMP. The illustration, Fig. 245, on the opposite page represents _the first practical steam pump ever made_; on pages 67-69 will be found an interesting account of it. The water end is _single acting_; the steam end is, of necessity, _double acting_ to produce the reciprocating motion. From this original design has been evolved the piston valve as well as many other designs of valve motion for pumps. Having already taken up in some detail the construction of “the parts of the pump” and the necessary appliances connected with its use, it now remains to consider the means by which the steam power generated is made available and the mechanism by which the energy is _transformed from pressure into pumping power_. It may be well to consider at some length the “Steam end” of the pump. This consists primarily of cylinders, together with their connections; _these constitute the muscular system of the pump_. The muscular or operating end is separate and distinct from the water end so far as construction is concerned but in operation the two are closely allied. It is therefore necessary as well as convenient to unite them in one equipment and thus enable the propelling mechanism to furnish a constant source of power. So far as the elastic force of steam itself is concerned its history dates back to a period two hundred years B. C., when, as described by Hero, the force generated by steam was utilized for actuating certain devices constructed rather for curiosity than for any benefit which might be derived from their use. Very little advance was made in the construction of practical devices until the latter part of the eighteenth century when James Watt by his improvements placed the stationary engine on an operative basis and gave to the world what has proved to be the greatest invention of all time.