apparatus for teaching Afeckanics. 449 



Let one end of a lever, Fig. 7. with a wheel at one end of It, be hinged to the poft of 

 the frame, by means of a gudgeon driven or fcrewed into the poft. To prevent this lever 

 from deviating fideways, let a flip of wood be connefted with it by a nail, which (hall be 

 faft in the lever, but which moves freely In a hole in the rail. The other end of this flip 

 muft be faftened to a ftake driven into the ground at three or four feet from the lever, at 

 one fide of it, and towards the end in which the wheel is fixed, Fig. 10. which is a vue 

 cToifeau, in the fame manner as the treadle of a common lathe is managed, and as the 

 treadle of a loom is fometimes guided *. 



Experiment 1 1. Under the wheel of this lever place an inclined plane or half- wedge. 

 Fig. 7. on the wooden road, with rollers under it, to prevent fridlion f ; faften a rope to 

 the foremoft end of the wedge, and pafs it through the pulleys (P. 4. and P. 3.) as in the 

 fifth experiment. Let a boy draw the fledge by this rope over his flioulder, and he will 

 find, that as it advances it will raife the weight upwards ; the wedge is five feet long, and 

 elevated one foot. Now, if the perpendicular afcent of the weight, and the fpace through 

 which he advances be compared, he will find that the fpace through which he has pafled 

 will be five times as great as that through which the weight has afcended ; and that this 

 wedge has enabled him to raife five times as much as he could raife without it, if his 

 ftrength were applied, as in Experiment I, without any mechanical advantage. By making 

 this wedge in two parts hinged together, with a graduated piece to keep them afunder, the 

 Wedge may be adjufted to any given obliquity ; and it will be always found, that the me- 

 chanical advantage of the wedge may be afcertained by comparing its perpendicular eleva- 

 tion with its bafe. If the bafe of the wedge is 2, 3, 4, 5, or any other number of times 

 greater than its height, it will enable the boy to raife refpeftively 2, 3, 4, or 5 times 

 more weight than he could do in Experiment I, by which his power is eftimated. 



77.1^ Screw, 



Thefcreiv is an inclined plane wound round a cylinder ; the height of all its revolutions 

 round the cylinder taken together, compared with the fpace, through which the power 

 that turns it pafles, is the meafure of its mechanical advantage^. Let the lever, ufed in the 

 laft experiment, be turned in fuch a manner as to reach from its gudgeon to the fliaft of- 

 the Panorganon, guided by an attendant lever as before. Fig. 8. Let the wheel reft upon 



* In a loom this fecondary lever is called alamh, by miftake, for lam; from lamina, a flip of wood. 



f There fliould be three rollers ufed; one of them muft be placed before the fledge, under which it 

 will eafily find its place, if the bottom of the fledge near the foremoft end it a little floped upwards. To 

 retain this foremoft roller in its place till the fledge meets it, it fltould be ftuck flightly on the road with 

 two fmall bits of wax or pitch. 



J Mechanical ad-vantage is not a proper term, but our language is deficient in proper technical tentis. 

 The word ponjiier is ufed fo indifcriminately, that it is fcarcely poflible to convey our meaning, without 

 employing it more ftriflly. 



Vol. IV.— January 180 i. 3 M • the 



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