THE ROYAL ARTILLERY INSTITUTION. 
273 
Sheers. 
W 
The runner tackle and guys of sheers give the relation P = yjj, when two 
double blocks are used for the runner tackle, but when luff tackles are 
W 
employed P = -g-. 
The relation of the power to the weight in the working of the sheers may 
be calculated. 
1st. When a crab capstan is used to work the main fall ; 
.\ P : W :: 1 : 78. 
2nd. When the main fall is worked by a luff tackle; 
P : W :: 1 : 24. 
3rd. When a gyn windlass is used ; 
.\ P : W :: 1 : 118. 
The strain on the guy rope of sheers may be calculated by regarding the 
sheers as a lever. 
D 
A rope AD supports a pole OD resting on the ground at 0, and carrying 
weight W suspended from D, it is required to find tension of rope AD . 
Draw OP at right angles to AD, and DN to ON. 
The centre of gravity of the pole is at C\ the middle, as the pole is 
uniform. Draw CR perpendicular to ON 
Taking 0 as the axis of moments, 
OP x tension of rope = ON x W + weight of pole x OR 
Let 0 = the angle DON, 
a — the angle ODA , 
w = the weight of pole; 
then OP = OD sin a. 
ON = OD cos 6. 
OR = J ON = | OD cos 0. 
a) 
