6y8 POPULAR SCIENCE MONTHLY. 



burning of the metal — they have only come into commercial use for 

 very small powers. 



During the last thirty-five years gas engines have been per- 

 fected, and more recently oil engines, and in point of efficiency 

 both convert a somewhat larger percentage of the heat energy of 

 the fuel into mechanical energy than the best steam engines. All 

 successful oil and gas engines are at present internal-combustion 

 engines, the fuel being burned in a gaseous form inside the working 

 cylinder. 



Very numerous attempts have, however, been made to construct 

 internal-combustion engines to burn solid fuel instead of gas. 

 Some have been so far successful as to work with good economy in 

 fuel, but the bar to their commercial success has been the cutting 

 of the cylinder and valves by fine particles of fuel. This difficulty 

 is not present when the fuel is introduced in the gaseous or liquid 

 form, and hence the success of gas and oil engines; but could this 

 difficulty be overcome, the solid fuel would be the cheaper to use. 



Internal-combustion engines, gas engines, oil engines, cannon, 

 etc., owe their superior economy in fuel to the very high tem- 

 perature at which the heat is transferred from the fuel to the work- 

 ing substance of the engine, and consequently the great range of 

 temperature in the working substance of the engine. In steam 

 engines the temperature is limited by the practical difficulties of 

 deterioration of metal and materials involved in the construction. 



About fifteen years ago I was led by circumstances to investi- 

 gate the subject of improving the steam turbine. In recent times 

 several attempts had been made to apply steam turbine wheels of 

 the Hero and Bianca types to the driving of circular saws and fans. 

 The velocity of rotation with either of these types must necessarily 

 be very high in order to obtain a reasonable efficiency from the 

 steam, a velocity much in excess of that suitable for the direct 

 driving of almost all classes of machinery; gearing was considered 

 objectionable, and it therefore appeared desirable to adopt some 

 form of turbine in which the steam should be gradually expanded 

 in small steps or drops in pressure so as to keep the velocity of flow 

 sufficiently low to allow of a comparatively moderate speed of rota- 

 tion of the turbine engine. 



The method adopted was to gather a number of turbines of the 

 parallel flow type on to one shaft and contained in one case, the 

 turbines each consisting of a ring of guide and a ring of moving 

 blades, the successive rings of blades or turbines being graduated 

 in size, those nearer the exhaust end being larger than those near 

 the steam inlet, so as to allow a gradual expansion of the steam 

 during its passage through the turbines. 



