Kimball— Laws of Frictic 

 Table III. 



the following table only velocities and relative coefficients 

 Table IV. 



> (4) Friction of wrought iron journals in boxes of different mate- 

 rials.— In this course of experiments a modification of the fric- 

 tion brake was used. A description of the arrangement in one 

 series will serve for all the others. A shaft 1" in diameter was 

 adjusted so that it could be driven at almost any rate between 

 one revolution in two days and 1,000 in a minute. A hole was t 

 bored through a block of cast iron 3£"x3$"x If, and carefully 

 shaft; rigid iron rods were screwed into the top 

 vertical line 

 ogles to the shaft. Upon these rods slotted weighta 

 could be placed, and thus the pressure upon the shaft and the 

 center of gravity of the brake could be readilv adjusted. Upon 

 the front of the block a plane mirror was fastened, and before 

 -venient distance, were placed a scale and telescope. 

 When the shaft was turned, the friction between it and the 

 brake caused the latter to turn until the moment of th< 



-\ to that of the brake, and the angle at which this 

 equality was established could be read from the scale bv the 

 telescope As the center of gravity was alwavs adjusted so 

 that the brake never revolved through an an<rle of more than 

 three degrees, the scale readings were approximately propor- 

 tional to the coefficient of friction ; and since relative and not 

 absolute results were sought for, the labor of reduction was 



