^6 Apparatus for teaching Mechanics. 



in (he refiflancc, is always compenfated by the difference of fpace through which the 

 inferior pafles. 



The experiments which we have mentioned are fufSciently fatisfaftory to a pupil, as 

 to the immediate relation between the power and the refiftance 5 but the different fpaces, 

 through which the power and the tefiftance move when one exceeds the other, cannot be 

 obvious, unlefs they pafs through xrtuch larger fpaces than levers will permit. 



Experiment 5. Place the fledge on the fartheft end of the wooden road, Fig. 1. ; fallen a 

 rope to the fledge, and condudl it through the loweft pulley P 4, and through the pulley 

 P 3, fo as that the boy may be enabled to draw it by the rope paffed over his (boulder. The 

 fledge muft now be loaded, till the boy can but juft advance with fliort fteps fteadily upon 

 the wooden road; this muft be done with care, as there will be but juft room for him 

 befide the rope. He will meet the fledge exactly on the middle of the. road, from which 

 he muft ftep afide to pafs the fledge. Let the time of this experiment be noted. It is 

 obvious that the boy and the fledge move with equal velocity, there is therefore no mecha- 

 nical advantage obtained by the pulleys. The weight that he can draw will be about half a 

 hundred, if he weigh about 9 ftone ; but the exaft force with which the boy draws is to 

 be known by Experiment i. 



The Wheel and Axlei 



This organ is ufually called in mechanics, The axis in peritrochio. A hard name, which 

 might well be fpared, as the word windlafs or capftan would convey a more diftinft idea 

 to our pupils. 



Experiment 6. To the largeft drum, Fig. i. faften a cord, and pafs it through the pulley 

 P downwards, and then through the pulley P 4 to the fledge placed at the end of the 

 wooden road, which is fartheft from the machine. Let the boy, by a rope faftened to the 

 extremity of one of the arms of the capftan, and paffed over his flioulder, draw the cap- 

 ftan round ; he will wind the rope round the drum, and draw the fledge upon its road. To 

 make the fledge advance twenty-four feet upon its road, the boy muft have walked circu- 

 larly 144 feet, which is fix times as far, and he will be able to draw about three hundred 

 weight, which is fix times as much as in the laft experiment. 



It may now be pointed out, that the difference of fpace, paffed through by the power in 

 this experiment, is exa£tly equal to the difference of weight, which the boy could draw 

 without the capftan. 



Experiment 7. Let the rope be now attached to the fmaller drum ; the boy will draw 

 nearly twice as much weight upon the fledge as before, and will go through double the 

 fpace. 



Experiment 8. Where there are a number of boys, let five or fix of them, whofe power 

 of drawing (eftimated as in Experiment I.) amounts to fix times as much as the force of 

 the boy at the capftan, pull at the end of the rope which -was faftened to the fledge ; they 

 will balance the force of the boy at the capftan : either they, or he, by a fudden pull may 



advance, 



