272 APPLIED MECHANICS 
dead centre, and the connecting-rod has therefore anti-clockwise motion 
about the pin at A. Hence the friction axis must touch the friction 
circle of the pin at A above the axis of that pin. Still referring to the 
_ position (a), the angle ABC is diminishing, and will go on diminishing 
until the crank is at its outer dead centre, and the connecting-rod has 
therefore. anti-clockwise motion about the pin at B. Hence the friction 
axis must touch the friction circle of the pin at B below the axis of 
that pin. 
The student should now have no difficulty in reasoning out the 
positions of the friction axis for each of the remaining cases (0), (¢), 
and (d). 
238. Tower’s Experiments on the Friction of Journal Bearings. 
—The results of Mr. Beauchamp Tower’s experiments * showed that the 
coefficient of friction is approximately proportional to the square root of 
the velocity, and inversely proportional to the intensity of the pressure 
on °. where p- is the co- 
when the journal runs in an oil bath. Thus p= 
efficient of friction, v the velocity of the surface of the journal in feet 
per second, p the intensity of the pressure in. lbs. per square inch of 
projected area of the bearing, and c a coefficient which has the following 
values for the lubricants mentioned :—Olive oil, 0°289 ; lard oil, 0°281 ; 
mineral grease, 0°431 ; sperm oil, 0°194; rape oil, 0°212; mineral oil, 
0-276. 
For syphon lubrication »=c’/p, where c’ = 2°02 for rape oil. 
For pad lubrication, » is approximately constant, and equal to 0°01 
for rape oil. 
The following results were obtained by Mr. Tower with a steel 
journal 4 inches in diameter and 6 inches long, at a speed of 150 re- 
volutions per minute, or 157 feet per minute. The “brass” was of 
gun-metal, and embraced nearly one-half of the circumference of tlie 
journal, and was placed on the top. The lubricant used was rape oil. 
Method of Lubrication. /? Kb 
Oiltbath = fo! ape tigrBeRe tr oe ARE eam 0-0014 
Syphon lubricator . ; j i : 252 56-0698 
Pad under journal . ; : i 272 0:0090 
With the same journal Mr. Tower obtained the results shown in the 
annexed table at a speed of 20 
revolutions per minute, or 21 
feet per minute in a bath of |? -| 44 2 216 aE 
mineral oil. pw . | 000132 | 0-00168 | 0-00247 | 0 0044 
Mr. Tower’s experiments on 
friction at different temperatures 
indicate a very great diminution in the friction as the temperature rises. 
Thus, in the case of lard oil, taking a speed of 450 revolutions per 
* Proceedings of the Institution of Mechanical Engineers, 1883 and 1885, 
en ee ee Ae 
