The invention upon which Watt was to improve was at his hand.  A word in regard to its status at the moment will throw some light upon that of Watt and his creation.  Newcomen had, as we have seen, produced the modern type of steam engine as an original and wholly novel invention.  But this machine, marvelous as an advance upon pre-existing forms of the steam engine, was still, as seen in the light of recent knowledge and experience, exceedingly defective.  The purpose of a steam engine is to convert into usefully applicable power the hidden energy of fuel, stored ages ago in the earth, by transformation, through the action of vegetation, from the original form, the heat of the sun, into an available form for reconversion, through thermodynamic operations.  In this process of reconversion, whatever the nature of the machine used in the operation, there are invariably wastes, both of heat required for conversion into power and of the power thus produced.  That machine which effects the most complete transmutation of the heat supplied it into mechanical power, which wastes the least amount of heat supplied and of power produced, is the best engine, and constitutes an advance over every other.

It was this reduction of wastes that made the Newcomen engine so much superior to that of Savery.  The latter was by far the simpler and less costly construction; but its enormous losses, both of heat and of power, mainly the former, however, made it an extravagant expenditure of money to buy and use it.  The Newcomen engine, costly and cumbrous, comparatively, nevertheless wasted so much less heat and steam and fuel that no one could afford to buy the cheaper machine.  Before considering what Watt accomplished, we may find it profitable to examine into the nature of the wastes which characterized this later and better machine on which he effected his improvements.

The Newcomen engine consisted of a steam boiler, a steam cylinder, a beam and a set of pumps.  By making the boiler do its work separately, the engine acting independently, and the pumps as a detached portion of the mechanism, this inventor had reduced to an enormous extent those wastes of heat and of steam and of fuel which were unavoidable in the older machines in which all these parts were represented by a single vessel, or by two at most, in each element.  In the Savery engine, the steam entering first heated up the interior of the working vessel to its own temperature, and held it at that temperature in spite of the cooling influence of the water present.  This consumed large quantities of heat.  It then was compelled to surrender probably much greater quantities still to the water itself, coming in direct contact as it did with its surface.  If the water was agitated, either by the currents produced during its ingress or by the impact of the steam entering the vessel, this heating action penetrated to considerable depths and perhaps even warmed the whole mass very far above