354 A. S. Kimball— Laws of Friction. 



(4.) Friction of wrought iron journals in boxes or bearings 

 of different materials. 



m (1.) Sliding friction down an inclined plane.— A full descrip- 

 tion of the apparatus used, and some of the results obtained, will' 

 be found in this Journal, March, 1876 ; also in Van Nostrand's 

 Eclectic Engineering Journal, June, 1876. It is sufficient for raj 

 purpose to say that the sliding body was made to carry a smoked 

 glass, upon which was traced a waved line, which by direct 

 measurement gave the time of sliding and the spaces passed 

 over, from which it was easy to compute the corres 

 coefficients of friction. In the article referred to, no velocities 

 less than two feet a minute were examined. An extension of . 

 the same experiment, to the case of much lower velocities, 

 showed a curve concave toward the time line, indicating that 

 at these velocities the coefficient of friction was increasing. As 

 the velocities increased, the line changed its direction and be- 

 came convex toward the time line; thus giving in the limits 

 of one experiment a verification of the statements made above. 

 For further particulars respecting this method of experiment, I 

 refer to the article published in March of last year. 



(2.) Shdi„>i frntion ,it nnijnru, f,</nri(i,s <,,, it horizontal plane. 

 —A heavy pine plank, fifteen feet long, whose surface had been 

 ied, was carefully leveled on the floor of the laboratory. 

 i weight-box was mounted upon shoes which could be cov- 

 ered with the material experimented upon. To its forward end 

 a spring d\ manometer , V : - attached, aln-h was pulled by a 

 cord wound around a drum, which was made to revolve at a 

 i locity. The motive power was a fifteen horse-power 

 Corliss engine, belonging to our machine shop, whose fly-wheel 

 runs with great regularity at the rate of sixty revolutions a 

 minute. A shaft from the shop runs underground to the cellar • 

 beneath my laboratory, whence through several countershafts 

 the power is transmitted. to any part of the room. By means of 

 change pulleys, I can easily command a great range of veloci- 



The experiments were made by drawing the box along the 



plane at various velocities, and lvadimr the friction from the 



dynamometer. This combination answers very well for low 



not be easily stopped when the 



speed is great. J PP 



Several series of experiments were made, with wood on wood, 

 also with leather on wood. The results verify the first part of 

 rfih the 

 ! of the 



h,: 



