LOGGING- IN THE DOUGLAS FIE KEGIOIST. 
75 
them are frequently far beyond their normal capacity. To see them 
hauling logs larger than 10 feet in diameter and 21 feet in length 
oyer rough ground on a " straight " line is to marvel that they are 
not wrecked in a short time. That they are not is due to the fact 
that they are simply, compactly, and powerfully built of the best 
adapted material. The frame or bed of the machine, on which the 
security of all fastenings and the permanency of alignments of all 
working parts depend, is strong and rigid, being made of the heaviest 
standard section of steel beams spaced by heavy crossbars of cast iron 
or steel. 
Fig. 30. — Compound-geared yarding engine. 
Logging engines are equipped with high-pressure boilers of the 
vertical type, built of 60,000-pound flange steel. They have a work- 
ing pressure of from 150 to 200 pounds (generally 200 pounds), and 
are guaranteed to pass Hartford inspection. They range in size from 
48 inches in diameter and 96 inches in height to 80 inches in diameter 
and 153 inches in height. 
The extreme height, and high working pressure of these boilers, the 
limits of which have been reached, is the result of constant increase 
in the cylinder sizes. The width of the engine frame, by limiting 
the diameter of the boiler, has restricted the dimensions of the round 
fire box. resulting in too small a proportion of grate to heating sur- 
face. To overcome the steaming difficulties resulting from insuni- 
