7. Proper fitting of bearing surfaces (37). 8. The reducing of the rubbing surfaces in escapements as much as the nature of the materials will allow without abrasion in the course of time (55). ~44. Friction Between Surfaces Moving at Very Slow Speed~, has been investigated by Fleming Jenkin and J. A. Ewing. A contrivance, which would be very excellent with some improvement, for the determination of the amount of friction under such conditions, is given in a paper[8] read before the Royal Society of London. The arrangement employed by them was composed of a cast iron disk two feet in diameter and weighing 86 pounds. This disk, being turned true on its circumference, was supported by a spindle terminating in pivots 0.25 C. M. in diameter, the pivots resting in small rectangular bearings composed of the material the friction of which with steel is to be determined. A tracing of ink was produced on a strip of paper which surrounded the disk, the ink being supplied by a pen actuated electrically by a pendulum, as in the syphon recorder. As the traces thus left on the paper were produced without in any way interfering with the freedom of motion of the disk, they afforded a means of determining the velocity of rotation. The relative velocities of the pivot to the bearing surfaces varied from .006 C. M. to 0.3 C. M. per second, being the velocities met with in the various parts of time keeping devices. Experiments were made with the bearing surfaces successively in three different conditions: viz. 1, dry; 2, wet with water; and 3, wet with oil; and gave the following results: TABLE I. --------------------------------------------------------- SURFACES. | COEFFICIENT OF FRICTION. ------------------------------|-------------------------- JOURNAL. | BEARING. | DRY. | WATER. | OIL. -------------|----------------|--------|--------|-------- Steel | Steel | 0.351 | 0.208 | 0.118 " | Brass | 0.195 | 0.105 | 0.146 " | Polished Agate | 0.200 | 0.166 | 0.107 ---------------------------------------------------------