83 
and that this pitting was very marked at 700 pounds. The small pieces 
torn from the balls and races were very different in shape from the flakes 
torn from the shaft by the rolls. 
The diagram giving a comparison of the friction line of the two kinds 
of bearings shows the friction of the roller bearing to be more than twice 
as great as that of the ball bearing. Calculations from the figures taken 
during the tests gave the co-efficient of friction for the ball bearings used 
to be .00475, or less than one-half of one per cent., while that for the roller 
bearings was .014, or nearly one and one-half per cent. I have no doubt 
that if the shaft used was of steel, hardened and ground, as the rest of 
the parts were, that the friction would be reduced. As the shaft was torn 
by the rolls, new parts were brought into contact and a marked drop of 
the pull occurred. 
Bearina-TeEsting DyNAMOMETER. 
By M. J. Goupen. 
In making some tests to determine the amount of power lost by fric- 
tion in different forms of shaft bearings, so much trouble was experienced 
in separating the loss in other parts of the apparatus used from that in 
the part being tested, when the regular transmission type of dynamometer 
was used, that the apparatus described here was devised for that purpose. 
It was tried in various forms experimentally before the present form was 
adopted. One of the rougher forms was described here last year in con- 
nection with a report then made on some bearing tests. In such tests the 
whole friction is so small that it is difficult to separate the friction due 
; to the part being tested from that of the rest of the apparatus. 
The machine as now used consists of a cast iron frame, made heavy 
enough to be stiff and to absorb a large portion of the vibration due to 
the rapidly moving parts. To the top of the frame is bolted a cast-iron 
table with planed surface. On this table are bolted two carriages, shown 
in the illustration at (a), that are fitted with ball bearings, in which a 
spindle or shaft revolves. These bearings are used because of the ease 
of alignment with them, and by fastening a set collar on each side of 
