710 TRANSACTIONS OP SECTION G. 



The accelerometer therefore reads in one of the three directions of space only, 

 and is not affected by even violent movements in the other two directions. 



With this instrument the author has measured the road resistance of various 

 classes of road and has obtained figures varying from 50 to 210 lb. per ton. On 

 main line railways the resistance is usually from 12 to 30 lb. per ton, depending 

 on the speed. Measurements have also been made of the resistance to motion 

 when a motor car is coasting. In this way the h.p. and the engine friction can 

 be measured and a figure for the mechanical efficiency be obtained. 



The conclusions reached may be summed up as follows. By the use of the 

 accelerometer road resistances can be read off at sight ; the air resistance of various 

 shapes of car body can be determined; the b. h.p.- and i.h.p. of the engine can be 

 obtained for various speeds ; and it is possible to trace step by step the losses of 

 power in transmission to the road wheels. 



3. The Cyclical Changes of Temperature in a Gas-engine Cylinder near the 

 Walls. By Professor E. G. Coker, M.A., D.Sc. 



Experiments described in Engineering for October 1908 show that the tempera- 

 ture at, the inner surface of a small gas-engine is about 240° C, and the cyclical 

 variation is usually less than 10° -C. 



The steady conditions of low temperature at the wall-surface are maintained 

 by the jacket-water, although the explosion of the gaseous mixture produces very 

 great changes of temperature close to the walls. 



This variation has not hitherto been measured for a complete cycle owing to 

 the difficulties which occur in measuring the highest temperature of the explosion. 

 In order to obtain the cyclical variation near the walls, a couple was made of an 

 alloy of 10 per cent, iridium and platinum, with a pure platinum wire, and this 

 was secured in a metal plug so that it projected \ inch into the cylinder. On light 

 loads and weak mixtures the cycle remained unbroken, but near full load the 

 platinum wire melted. 



Couples made from 10-per-cent. alloys of iridium and rhodium with platinum 

 were afterwards used, having an electromotive force E above 500° C. given by 

 E = - 174 + 7-6075 T - 0*00167 T 2 , where T is the temperature centigrade. The 

 junctions were rolled down to five or six ten-thousandths of an inch thickness and 

 inserted at a depth of ^ inch from the cylinder-wall. 



These couples were able to withstand the highest temperatures near the walls, 

 and they were not melted except during abnormal explosions. 



Measurements of the cyclical variations showed a variation of E.M.F. lying 

 between 1*56 and 7'83 milli-volts with an average cold junction temperature of 

 30° C. The temperature variation corresponding to these values ranges between 

 250° C. and 1700° C. 



In estimating the highest temperature reached, the upper limit of temperature 

 is indicated by the partial melting of one of the wires when the engine ran above 

 its full normal load, and the lower limit is indicated by the melting of platinum 

 wire. The melting-point of platinum is 1710 ± 5° C, and, in the absence of 

 defipite values of the melting-points of the alloys used, it is assumed that both 

 are below the melting-point of iridium, for which Violle's value is 1950° C. The 

 probable causes of error in the measurements are discussed, and the conclusion is 

 reached that the temperature at the place of measurement has a maximum value 

 between 1850° and 1900° C. 



4. The Value of Anchored Tests of Aerial Propellers. 1 By W. A. Scoele. 



Joint Discussion with Section A on the Principles of Mechanical Flight. 

 Opened by Professor G. H. Bryan, F.R.S. 



Published in Engineering, September 9, 1910. 



