Nikola Tesla U.S. Patent 514,169 - Reciprocating Engine Patent Wrapper Page 23

68 2 " pressure, and an air spring ma intained in vibration by the movements of the piston, the piston and spring being related in substantially the mammer described so that the forces which tend to bring the reciprocating parts in to a given position are proportionate to the displacements whereby an isochronous vibration is obta in ed. 3. The combination of a cylinder and a piston adapted to be reciprocated by steam or gas under pressure, a cylinder and a plunger therein reciprocated by the piston and constituting an air spring acting upon said piston, the piston and spring being related in the manner described so that the forces which tend to bring the piston into a given position are proportionate to the displacement whereby an isochronous oscillation of the piston is obtained." With regard to the criticism made by the office as to the impossibility of developing heat in the cylinder etc. we submit that we cannot comprehend the nature this object ion. The cylinder may be made so hot as to melt metal. This depends entirely upon the degree of compression of the air within it. It is perfectly well known that heat is developed by the compression of air. This is illustrated by the old and familiar experiment of attaching an inflammable substance to the under side of a piston and then forcing the piston down into a cylinder. It is very easy to ignite the material attached to the piston in this way by the increase in temperature of the air compressed. In fact this device is sometimes -2