Nikola Tesla U.S. Patent 517,900 - Steam Engine Patent Wrapper Page 10

82 rod which does not require to be very close fitting, and constitutes an ordinary form of air spring. Lif steam or a gas under pressure be admitted through the port c to either side of the piston b, the latter, as will be understood, may be maintained in reciprocation, and it is free to move, in the sense that its movement in either direction ceases only when the force tending to impel it and the momentum which it has acquired are counterbalanced by the increasing pressure of the steam in that end of the cylinder towards which it is moving, and as in its movement the piston has shut off at a given point, the pressure that impelled it and established the pressure that tends to retum it, it is then impelled in the opposite direction, and this action is continued as long as the requisute pressure is applied. The movements of the iston compress and rarify the air in the cylinder i at opposite ends of the seme alternately, and this results in the heating of the cylBut since a variation of the temperature of the air in the chamber would affect the rigidity of the air spring, I ma intain the temperature uniform as by surrounding the cylinder with a jacket a' which is open to the air and filled with water. inder, TO In such an engine as that just above described the normal pressure will produce a stroke of determined length, -5