92 Prof. B. HopkinsoD on the 



temperature, or 31°*. This agrees pretty well with the 

 temperature shown by the thermometer at this point, that 

 is 34°. It is not to be exnected that the agreement will be 

 absolute because the air will have received some heat from 

 the cylinder-walls, which have a temperature of 40° C. 



The inlet-valve closes at crank-angle 25° (25° after the out- 

 -centre). The pressure is then almost exactly atmospheric, 

 the temperature calculated from the wire thermometer is 

 37° C, and the volume is 1'45 cubic feet. From these data 

 the mean temperatures can be calculated from the indicator 

 diagrams at any point of the compression and expansion 

 strokes until the exhaust-valve opens. It will be useful to 

 compare the temperatures so calculated for one or two points 

 with those given by the thermometer (curve C). At the 

 in-centre (crank-angle 180°), the pressure reaches its maximum 

 value of 173 lbs. absolute. The volume is then 0*236 cubic feet, 

 and the mean temperature calculated from the pressure and 

 volume is 



173 0-236 x310 = 5 ( )0 o Absolute, or 317° C. 

 14-7 1-45 



The temperature obtained from the thermometer is 320° C, 

 but the correction here is about 100°, so that the possible 

 error is considerable. The temperature near the wire is 

 certainly above the mean, since the gas is losing heat to the 

 cylinder-walls, and the layer in contact with the walls must 

 be colder than the remainder. If we suppose that the gas in 

 the neighbourhood of the wire has been compressed without 

 loss of heat, the temperature there will be 



(ut)' ^ X 310=G28 ° Absolute, or I 



]55 : C. 



The gas-temperature curve during expansion is, as it should 

 be, nearly symmetrical with the compression portion. The 

 pressures in expansion are slightly less than at the corre- 

 sponding points in compression by reason of the loss of heat 

 to the cylinder- walls ; but the consequent differences of tem- 

 perature are too small to be certainly indicated, especially in 



* If 6 be the rise of temperature the volume of air drawn in per stroke 



is of the stroke volume, since the absolute temperature in the 



G+290 ' ,. r * 



inlet-pipe is 290°. The work done is 360 foot-pounds per cubic toot of 



stroke volume, or 36 ° -~ 9 - per cubic foot of air drawn in. We have there- 

 fore 360x29 ° ^ e = ]4°4. 

 (61+290)24 



