The Trials of Ploughs at WcorwicJc. 
310 
between the speed of the driving wheel and the drum being 
such that for every run of one hundred yards’ travel in ploughing 
the drum moves 4’0156 inches. An indicator paper is wrajiped 
round the drum, and a pencil fixed to the framing of the instru- 
ment — mounted on a spring to give sufficient pressure on the 
paper for marking — draws a line the length of which indicates 
the length of run, and it also represents the zero line from 
which the amount of draught is measured, as described later. 
For reading off at once the distance travelled, a ring with a 
graduated scale is mounted on one end of the drum. At the 
commencejnent of a trial the zero on this scale is set opposite to 
a fixed pointer, the ring is then clamped to the drum, and 
revolves with it. At the end of the run the actual distance may 
at once be read off opposite to the pointer. In tliis way a 
duplicate register of the distance travelled is obtained. 
In order to measure the draught a draw-bar passes from end 
to end of the dynamometer, the back end being provided with a 
hook for the attachment to the plough. On this draw-bar are 
mounted two spiral springs, one end of each of which bears 
against a disc keyed on to the draw-bar, while the other ends 
bear against the cross-framing of the dvnamometer. It will 
thus be seen that, if a load is attached to the hook of the draw- 
bar and the dynamometer is pulled forward, the springs will 
be compressed in proportion to such load, and that the draw-bar 
will be given a certain travel corresponding "with such compres- 
sion. This travel is I’egistered on the paper on the brass drum 
already described by a second pencil mounted in connection 
with the draw-bar. In this way, as the drum revolves a diagram 
is obtained, the fixed pencil drawing a straight line representing 
the distance travelled, while the other pencil, drawing an irregu- 
lar curve, or, more correctly speaking, a zig-zag line, the depres- 
sions and elevations corresponding to the various fluctuations in 
draught. As, at starting, both pencils are set on the same line, 
it is only necessary to measure the vertical distance from the 
straight line drawn by the fixed pencil to any point of the 
upper curved line, and this will represent the draught at that 
particular point. A mean of a series of such measurements will 
represent the mean draught. 
A further provision for recording the mean draught is made 
by means of integrating gear. A vertical gun-metal disc is 
actuated through the chain gearing from the main driving 
wheel ; against the face of this disc works a small gun-metal 
roller wheel free to slide on a square spindle mounted in connec- 
tion with the main draw-bar. As this small wheel revolves it 
rotates the square spindle, one end of wdiich is connected up 
T 2 
