3i6 REPORT— 1902 



of four positions such that the pressure on the plunger is equal to one 

 two, four, or eight times the pull exerted on the castor frame. By having 

 this arrangement it is possible to use the apparatus through a very wide 

 range of experiments, say for tractive efforts of from 5 to 500 lb. 



Plunger. — The plunger E, which is 2-6 inches diameter, presses upon 

 a rubber diaphragm enclosing a space filled with water, and it is the pres- 

 sui'e exerted on this water that is autographically recorded. Two pipes 

 are connected to the water space, one for transmitting the pressure to the 

 gauge G (Plate V.), the other being used for filling the system. An ordi- 

 nary rubber bulb off a motor horn is filled with water and connected to 

 this latter pipe, so that when the bulb is squeezed by the hand the water 

 is forced through the system, and out of a small hole in the end or the 

 Bourdon tube. By this means all the air is expelled, and when sure that 

 such is the case the system is closed and the water retained. 



Recording apjMratus. — The recording appai'atus was placed in the 

 hands of Messrs. Schaffer and Budenburg, Ltd., Manchester, who have 

 turned out a very good instrument. This apparatus is a combined re- 

 cording pressure-gauge G and tachometer H (Plates IV. and V.) mounted 

 on one base and recording on the same horizontal drum K, which carries 

 a band of paper, LL, 8^ inches wide, the graph of tractive effort-space 

 being at one side of the paper, while that of velocity-space is at the other 

 side. This drum is driven off the tachometer spindle, and its motion 

 therefore is in accordance with the motion of the car, a length of 10-3 feet 

 of the paper corresponding to a mile of road. The makers have worked 

 out a very neat parallel motion, so that the ordinates of both graphs are 

 straight. 



The instrument is mounted in a rain-proof glass case, supported on a 

 pneumatic cushion, N (Plate III.), the drive to the drum and tachometer 

 being through a flexible shaft. This arrangement has worked very well, 

 fairly steady curves being olitained even over rough roads at high speeds. 

 Stops are provided to prevent too great a movement of the levers, thus 

 ensuring against undue shocks on the gauge. 



If found necessary an arrangement can be attached for marking seconds 

 on the paper. 



A revolution counter is provided for olitaining independently the 

 revolutions of the experimental wheel : this will act as a check on the 

 record. 



XIV. Nature and Scope of the Experiments hy the Committee. 



Experiments will be conducted to determine the relation between the 

 tractive effort and the following, viz., load, diameter of wheel, width and 

 section of tyre, hardness of tyre (in the case of pneumatics), effect of 

 springs, and velocity for every type of road under all circumstances, and 

 any other relations that may be suggested during the progress of the 

 ■work. 



In performing an experiment a given type of wheel is mounted 

 in the frame and a run made over a piece of road of the desired type. 

 Since the two graphs are side by side the relation between tractive 

 force and velocity can be seen at every point of the run, and from those 

 portions of the graph where the velocity is constant and of the required 

 value, a mean tractive effort can be obtained. After a number of ex- 

 periments have been perfoi-med, curves can be plotted and empirical 

 formulae deduced for the various relations, 



