XCII. HERBERT E. ROSS. 
the strength of a double ply. The double belt with flexible back 
is used for larger pulleys with much crown, thus giving a better 
grip on the pulley. 
Is has been customary to refer to the slight movement of the 
strap with reference to the pulley as slip. The author would 
prefer to designate this action as creep, leaving the former defini- 
tion to represent the actual failure of the belt. 
The creep in belts examined by the author varied as follows, 
from no load to maximum :— 
Leather... fe os ith 2°47 
Rubber ... a os eo 
ens a ees ; 5 2v 
Balata ... eee cy Oi aet 
From the comparison already referred to, the creep in ropes 
may be taken at 1%. 
For durable life the most economical speed for leather belts 
may be taken at :-— 
3000’ per minute for triple. 
2500’ - », double. 
2000’ Hf » single, 
The maximum speeds for any degree of durability being 6000, 
5000, and 5000 per minute respectively. 
» 
It would seem to be practically impossible to use belts at these 
speeds, except at certain distances between centres of over 20’. 
The author is of opinion that where many revolutions are required 
the tendency to reduce the size of the pulleys is the cause of much > 
vibration and wear due to the shock, and consequent wave due to 
the joint crossing the pulley. Under such disadvantagous circum- 
stances, the best belts may only last a few weeks. Pulleys not 
less than 12” diameter for a double belt and 8” for a single belt 
are desirable where reasonable wear is expected. 
_ The keen competition among machine builders has resulted in 
reducing the diameter of the pulleys in slow moving machines, 
and cases are common where wide belts are used on pulleys of 
