\i4 Account of some Experiments on Friction. 



a velocity = 32,V x 60 = 1950 feet per second at the end 

 of" one minute to a body falling freely, or 1 17000 feet per 

 minute; and the, accelerating or retarding power bcina; as 

 the velocity acquired or destroyed in a given time, we hiive 

 117000 : 3.57-^- :: \"iQ : 5,35 = the power in pounds' 

 applied at the circumference of the stone that would ge- 

 nerate or destroy the velocity of 26 turns per mi/ud'j. 



The resistance arising from friction is not, in the expe 

 riments, applied at the circumference of the stone, but at 

 that of the rubbing parts of the spindle, which, as before 

 stated, was 3 V inches diameter ; therefore to find the actual 

 resistance caused by friction, 5,35lb. is to be increased in 

 the inverse ratio of the diameter of the stone to that of the 

 pivots : hence, 3,123 : 52,5 : : 5,35 : QOlb. nearly, the re- 

 sistance arising from the frictior^ of 3700!b. of matter, or 

 less than vnc-Jwlieth part of the weight. 



I purposely omit to take into account the resistances of 

 inertias of the iron spindle and wooden pulley, because the 

 former from its centric situation, and the latter from its 

 lightness, would not materially afiect the conclusion. 



It may now be judged of in some degree, whether the 

 greater resistance which appeared to retard the stone under 

 greater velocities might not arise f.-om the air. It has been 

 shown that the mean least and mean greatest retardations 

 per minute were 26 and 30^ revolutions ; if 26 turns be 

 equivalent, as shown above, to 5,35ib., at the circumfe- 

 rence, 304 are equivalent to 6,3 lib. and the difference 96ib. 

 would cause this extra resistance. Thsit a stone of the dia- 

 meter specified, whose sides were very roughly hewn, anc| 

 which moved in a trough nearly half its depth with a velo- 

 city of upwards of 60 feet per second, should meet with a 

 resistance from the air equal to not quite one pound weight 

 at its circvmiference, is not with mc a matter of surprise, 

 and I have no hesitation in attributing the variations in the 

 niean second differences to this cause. 



It will be evident, on due consideration of the facts which 

 occurred at the end of each experiment, thai, the resistance 

 was mucii greater in the last portion of time of each that) 

 in the previous ones ; and though part of this might arise 

 from the small velocity of the rubbing surfaces at that pe- 

 riod of the experiments, part might also arise from a cir-*- 

 rumstance vv'hich was obvious enough, viz. the stone being 

 jicavier on one side of the centre than on the other, so that 

 the motion in the latter seconds of time was considerably 

 irregular. 



On the whole_, I conclude that the^e expcrintcnts con- 

 3 firm 



