Measurement of Gas-Engine Temperatures. 87 



who are desirous or! measuring gas-engine temperatures. The 

 conclusion at -which I have arrived is that by the use of this 

 method of correction and sufficiently accurate measurements 

 of resistance, the temperature of the gas can be obtained 

 within a few degrees with a wire j^q-q inch in diameter, if the 

 wire does not melt. But in large engines using high com- 

 pression, a wire of this size will inevitably melt; and if still 

 thicker wire be used, the correction for time-lag becomes 

 unmanageably large. It appears that the measurement 

 of temperature in such engines by this means is a very 

 difficult operation, involving measurements of accuracy far 

 exceeding that of the ultimate result, unless wires of a more 

 refractory metal than platinum be used. 



The briefest description of the gas-engine on which the 

 experiments were made is all that is necessary. It is one 

 of Messrs. Crossley Bros", well-known Otto cycle-engines, 

 having a cylinder 11J inches diameter, and a stroke of 

 21 inches, and it gives about 40 H.P. when running at 

 185 revs, per minute. The compression space is 407 cub. ins. 

 or ^i- of the stroke volume, and the gases are compressed to 

 about 170 lbs. per square inch absolute before firing. The 

 engine has been lent to the Engineering Department of 

 Cambridge Universitv through the kindness of Mr. F. W. 

 Crossley. For the purpose of the experiments to be described 

 it was belted to a dynamo (lent by Messrs. Mather & Piatt, 

 Limited) by which it was driven, the gas-supply being cut off. 

 Thus the engine drew in a charge of air through the air inlet- 

 valve, compressed it to 173 lbs. per sq. in., expanded it again 

 down to near atmospheric pressure, and expelled it through the 

 exhaust-valve. 



The thermometer is a piece of bare platinum wire, y 4 oo i ncn 

 in diameter and 29 centims. long. Its ends were hard-soldered 

 to thicker platinum wires which were sealed into glass tubes 

 passing through the exhaust- valve cover and projected about 

 U^y of an inch into the compression-chamber of the engine. The 

 wire was threaded througlra hole in a thin mica plate, the plate 

 being carried on the end of a steel rod 5 inches long and -^ inch 

 diameter, which was screwed into the exhaust-valve cover and 

 projected into the compression-chamber. Thus the wire was 

 supported in the form of a V, the ends being 2£ inches 

 apart and close to the walis of the compression-chamber and 

 the apex in the centre of that chamber. The exhaust-valve is 

 in the floor of the compression-chamber immediately below 

 the wire. The inlet- valve is in the side of the compression- 

 chamber. During the suction and exhaust strokes the motion 

 of the air about the wire is violent and turbulent owing to its 



