Savery had created his vacuum by the condensation of steam in a closed vessel by dashing cold water against it. Papin had created his vacuum by exhausting the air in a cylinder, fitted with a piston, by means of an air pump. What Newcomen did was to combine both systems. Instead of employing Savery's closed vessel, he made use of Papin's cylinder fitted with a piston, but worked by the condensation of steam, still employing the clumsy system of dashing cold water against the cylinder.
Whilst the engine was still in its trial state an accident occurred that led to another change in the mode of condensation. It was this. In order to keep the cylinder as free from air as possible, great pains were taken to prevent it from passing down with the piston, and to keep the cylinder air-tight, water was employed to lie above the place where the piston passed up or down.
At one of the early trials the inventors were surprised to see the engine make several rapid strokes, and on looking into the cause found that there was a small hole in the piston, which allowed a jet of cold water to penetrate within, and that this acted as a rapid condenser of the steam.
A new light suddenly broke upon Newcomen. The idea of condensing the steam, and so producing a vacuum by injecting cold water into the receiver, instead of splashing it against the outside, at once occurred to him; and he proceeded to embody the principle which this accident had suggested, as part of his machine.
Another improvement was due to another accident, if so it may be termed. To keep the machine in action a man or boy had to be employed in turning alternately two taps, one admitting the steam into the
