682 Report on the Trials of I?7iplcments at Bedford. 



that if the small disc makes one revolution when it is 1 inch from 

 the centre of the large one, it will make two revolutions if it 

 be 2 inches removed. This small disc communicates with a 

 mechanism by means of which the mean draught is indicated. 



The saddle-chain is hung over the saddle-plate r, and attached 

 to the ordinary shaft hooks on either side. The saddle-plate is 

 hung from one end of an equal-armed lever, Q, to the other end 

 of which is attached a spring balance, E, the movements of the 

 indicator being noted by an assistant who walks alongside. 



The weight thrown upon the draught-plate by the vertical 

 component of the pull is received by the castors, and duly taken 

 into account. 



No transverse components of angular pulls, whether in a 

 horizontal or vertical direction, are communicated to the spindle, 

 for the draught-plate E, with its joints and castors, will transmit 

 the direct horizontal components only. 



The instrument is supplied with three pairs of springs, suited 

 for maximum loads of 500, 1000, and 2000 lbs. respectively. 



The following explanations may be considered in connection 

 with the first column in the Tables showing the results of the 

 trials (pp. 700, 701). The waggons were weighed on two weigh- 

 ing-machines, placed near each other, so that first the pair of fore 

 wheels and then the hind pair were weighed. These weights are 

 recoi'ded in lines 4 and 5 and their sum in line 6. The waggons 

 were then loaded and again weighed as before ; this we find in 

 lines 7, 8, and 9, while the weights of useful load are given in line 

 10. The maximum load per inch-width of tyre is given in line 

 13. The gauge width of wheel-centres on the ground in line 

 18 is the distance between the centres of the two fore wheels, 

 or of the two hind wheels. The wheel base, given in line 19, 

 is the horizontal distance between the centres of the fore and hind 

 wheels on either side of the waggon. Each waggon and cart 

 was attached to the horse dynamometer as already described, and 

 drawn along the macadamised road for 200 yards. The mean 

 draughts in pounds there registered are recorded in line 23. 

 The mean draught per ton gross load in line 24 is calculated 

 by dividing the pounds draught in line 23 by the weight in 

 tons line 9 ; while the mean draught per ton of useful load in 

 line 25 is calculated in a similar manner fi'om the tons of useful 

 load found in line 10. 



The mean draught in pounds registered when passing over 

 the field course and reduced to a level road, will be found in 

 line 23, while the figures in lines 28 and 29 are obtained as 

 already described in the case of the macadamised road. 



The draught of any carriage is made up of friction at the axle 

 and resistance on the road. When the axles are well lubricated, 



