203
OF ENGINEEBINü FOKMULÆ.
Notes on Permanent Way— continued.
The force required to produce lateral displace-
ment is directly proportional to the weight by
which sleepers are pressed on the ballast.
If the ballast be not filled in at the ends of the
sleepers, the elasticity of the rail will bring back
sleepers to their original position, even atter
considerable displacement.
SPIKES.
Spikes driven for the first time have a greater
holding power than those which have been driven
aud drawn several times.
Bellied spikes have only from -7 to *9 the
adhesion of straight spik'es of the same weight.
No advantage is gained by jagging or twisting
spikes.
The points of spikes should be “ chisel ” form,
so as to displace the grain of the timber endways.
The best proportion for the point of a spike is
length — twice its breadth.
Straight spikes are preferable to those of tapei
form.
SLEEPERS.
Too long a bearing of the rail on the sleepers
causes the sleepers to rock.
Distance of joint sleepers apart should be • 6 of
the distance apart of the intermediate sleepers.
Sound sleepers of fir are compressed ‘04 inch
by a pressure of 80 or 100 lbs. per square inch,
or by 60 lbs. after the sleeper has been subject
to compression for some time.