TRACT 36.

THE WHIRLING-MACHINE.

165

“ Round the barrel bcde there is wound a fine silk line,the turns of which appear in the figure, and after this linehas taken a sufficient number of turns, it is conducted hori-zontally to the pulley l, over which it is passed, and then aproper weight M is hung to its extremity. If this weight beleft at liberty, it is obvious, that it will descend by its owngravity, and will by its descent turn round the barrel bcde,together with the arm gh and the body p fas'ened to it.And while the resistance on the arm gh and the body p is lessthan the weight m, that weight will accelerate its motion,and thereby the motion of GH and P will increase, and con-sequently their resistance will increase, till at last this resist-ance and the weight m become nearly equal to each other.The motion with which m descends, and with which the bodyp revolves, will not sensibly differ from an equable one.Whence it is not difficult to conceive, that by proper obser-vations made with this machine, the resistance of the body pmay be determined.

4. “ The most natural method of proceeding in this in-vestigation, is as follows. Let the machine have first ac-quired its equable motion (which, as will hereafter appear,will be usually attained in 5 or 6 turns from the beginning)and then let it he observed, by counting a number of turns,what time is taken up by one revolution of the body p ; thentaking off the body p and the weight m, let it be examined,what smaller weight will make the arm gh revolve in thesame time, as when p was fixed to it; this smaller weightbeing taken from m, the remainder is obviously equal in ef-fort to the resistance of the revolving body p; and this re-mainder being reduced in the ratio of the length of the arm.to the semi-diameter of the barrel, will then become equalto the absolute quantity of the resistance. And as the timeof one revolution is known, and consequently the velocityof the revolving body; there is thereby discovered, the ab-solute quantity of the resistance to the given body f, movingwith a given degree of celerity.

5. <f And note, that to avoid all exceptions, I have gene-