Nikola Tesla U.S. Patent 517,900 - Steam Engine Patent Wrapper Page 11

which may be increased or diminished according to the increase of pressure about or the reduction of pressure below the normal and due allowance is made in constructing the engine for a variation in the length of stroke. The rate or period of reciprocation of the piston, however, is no more dependent upon the pressure applied to drive it, than would be the period of oscillation of a pendulum perme rently maintained in vibration, upon the force which periodically impels it, the effect of variations in such force being merely to produce corresponding variations in the length of stroke or amplitude of vibration respectively. The period is mainly determined by the rigidity of the air spring and the inert ia of the moving system and I may therefore secure any period of oscillation within very wide limits by properly proportioning these factors, as by varying the dimensions of air hamber which may be equivalent to varying the rigidity of the spring, or by adjusting the weight of the moving parts. This latter is readily accomplished by making provision for the attachment to the piston rod. of one or more weights h'. Since the only work which the small engine has to perform is the reciprocation of the valve attached to the piston rod, its load is substantially uniform and its period by reason of its conWhatever tray be the load struction will be constant. on the main engine therefore the stean is admitted to the -683