CATALOG OF THE MECHANICAL COLLECTIONS I53 



of combustion, the working piston will by atmospheric pressure be 

 caused to perform its forward stroke, the back loose piston traveling 

 with it. On approaching the front loose piston the back loose piston 

 is arrested in its motion while the working piston completes its 

 stroke, moving close up to the front loose piston and expelling the 

 products of combustion from between them, while at the same time 

 a charge of gas and air is drawn into the space formed between the 

 working piston and the back loose piston. On the charge being 

 exploded, the back loose piston is thrown to the back end of the 

 cylinder and the working piston performs its back stroke, together 

 with the front loose piston, and the operation is repeated as above 

 described. 



GILLES GAS ENGINE, 1876 



U.S.N.M. no. 311362; original patent model; transferred from the United States 

 Patent OflBce ; not Illustrated. 



This model was submitted with the application for the patent issued 

 to Friedrich W. Gilles, of Kalk, Germany, July 11, 1876, no. 179782. 



The engine represented by the model is a 1-cy Under vertical gas 

 engine employing two pistons, a working piston (the lower one) and 

 a loose piston (the upper one). The loose piston was intended to fly 

 to the top of the cylinder where it would be caught and held, produc- 

 ing within the cylinder a reduced pressure, which would cause the 

 work piston to return under the pressure of the atmosphere and thereby 

 perform work on the return stroke as well as the explosion stroke. 

 Provision was made to cushion the free piston at the top of its stroke 

 for the purpose of quiet running. The combustible mixture was drawn 

 in and ignited on the explosion stroke without compression. 



OTTO GAS ENGINE, 1877 



Plate 32. Fiqukb 1 



U.S.N.M. no. 251284 ; original patent model ; transferred from the United States 

 Patent Office ; photograph no. 18623A. 



This model was submitted with the application for Patent no. 

 194047, issued to Nicolaus Otto, of Deutz, Germany, August 14, 1877. 



This patent was the first issued for a 4-stroke cycle engine in this 

 country and marks the introduction of this important engine here. 



The model shows a horizontal single-acting piston engine, with a 

 lay shaft, driven by bevel gearing from the crankshaft, extending to 

 the head end of the cylinder. The lay shaft terminates in a crank 

 that operates a slide valve across the head of the cylinder. A cam on 

 the lay shaft operates through a crank a drop valve on the opposite 

 side of the cylinder, and a centrifugal governor is driven from a gear 

 on the lay shaft. The cylinder is water- jacketed. The slide valve acts 



49970 — .39 11 



