FRICTION OF ROPES.

219

w s

Whence we liavc = 400 lbs. or G — F' = 400 lbs.

rr

Then, by Theorem E t — '^ • ^1 * — 152 seconds.

’ 3 V (G — F') X r

By Experiment XIV., when the moving-force and resistance were in a state of dynami-cal equilibrium, the time of descent was 200seconds. In practice as above, we find that inorder to effect the certain transit or passage, itis necessary that the preponderance should besuch as that, under the most favourable wea-ther, the descent should be effected in 152seconds ; then the excess or preponderance ofgravitating power to be given in practice abovewhat is required to merely effect the descentin fine weather, or by taking the resistance asshewn in the table, must be in the ratio of200 152, or in even numbers as 4 : 3.