THE ROYAL ARTILLERY INSTITUTION. 
125 
Effective pressure of the lever (acting with its own weight) at W % 
44*375 x 29*12 
= — -—— = 420*73 lbs. 
Equivalent weight, if applied at the extremity of the long arm, 
430*73 
20 
= 21*536 lbs, 
Weight of small scale pan, &e. 21 lbs. 
Total pressure at TF, due to (21 x 21*536) acting at the end of long arm, 
= (21 x21*536) 20 =850*7 lbs. 
Weight to be placed in scale pan, to produce A 
1120-850*7 
a ton pressure at TF. 
20 
= 13*5 lbs. 
Eor every additional \ ton it was requisite to place \ cwt. in the scale 
pan. 
Beyond the above, *55 lb. was needed in the scale pan to balance the 
weight of table, &c. at TF. 
The gain of the leverage, ascertained by experimenting with various 
weights of the segment and pulley arrangements 2*/,?was 4*96 : 1, therefore 
the weights placed in the large scale pan + the weight of the scale pan, &c. 
X 4*96 = R in the tables. 
Description of the experiments . 
Series a. 
TO ASCERTAIN THE EPPECT OP VAEYING THE AMOUNT OP SUBPACE. 
The woods used in this series were English oak, elm, East Indian teak, 
and yellow pine; the metals were wrought-iron and gun-metal; and the 
whole were carefully surfaced. 
A constant pressure of 2240 lbs. was used throughout, on “ two ” sliding 
surfaces; the results are given in Tables I. to Y1II., Table YII. being a 
general summary of the results, and Table YIII. a statement of the con¬ 
dition of the materials after pressures of 140 lbs. and 560 lbs. to the square 
inch respectively. 
Erom these experiments it appears that the amount of surface has no 
direct effect on the coefficient of friction of motion, but the small surfaces 
require a more violent shock to set them in motion; and when the amount 
of pressure per square inch exceeds 140 lbs. abrasion is liable to commence, 
and therefore the surfaces of any compressor for a gun carriage should be 
sufficiently large to allow of the pressure necessary to check the recoil not 
exceeding 80 to 120 lbs. to the square inch, 
