fig. 4. Thus, while the inclined plane is moved i 

 through the distance C B, the beam is raised 

 through the^hight C A. 



When the inclined 

 plane is applied in 

 this manner, it is 

 called a vredge. — 

 And if the power 

 applied to the back 

 were a continued 

 pressure, its propor- 

 tion to the weight 

 w^ould be that of A 

 Cto CB. It follows, 

 therefore, thiit tlie 

 more acute the angle 

 B is, the more pow- 

 erful -will be the 

 wedge. > 



In some cases the wedge is formed of two in- 

 cUned planes, placed base to base, as represent- 

 Tlie theoretical estimation of the 

 power of this machine is not ap- 

 plicable in practice with any de- 

 gree of accuracy. This is in part 

 owing to the enormous propor- 

 tion which the friction in most 

 \ cases bears to the theoretical value 

 ■ of the power, but still more to the 

 nature of the power generally 

 used. The force of a blow is of a 

 nature so wholly diffei^nt from 

 continued forces, such as the press- 

 ure of weights, or the resistance 

 offered by the cohesion of bodies, 

 that they admit of no numerical 

 comparison. Hence we cannot 

 properly state the proportion 

 which the force of a plo\v bears to the amount 

 of a weight or resistance. The wedge is almost 

 invariably urged by percussion, while the re- 

 sistances which it has to overcome are as con- 

 stantly forces of the other kind. Although, 

 however, no exact numerical comparison can 

 be made, yet it may be stated in a general way 

 that the wedge is more and more powerful as 

 its angle is more acute. 



In the arts and manufacturers, wedges are 

 used where enormous force is to be exerted 

 tlirough a very small space. Thus it is resorted 

 to for splitting masses of timber or stone. Ships 

 are raised in docks hy \vedges driven under 

 their keels. The ^vedge is the principal agent 

 in the oil-mill. The seeds from which the oil is 

 to be extracted are introduced into hair bags, 

 and placed between planes of hard \vood. — 

 Wedges inserted bet\veen the bags are driven 

 by allowing heavy beams to fall on them. The 

 pressure thus excited is so intense, that the 

 seeds in the bags are formed into a mass nearly 

 as solid as wood. Instances have occurred in 

 vs-hich the \vedge has been used to restore a tot- 

 tering edifice to its perpendicular po.sition. All 

 cutting and piercing instruments, such as knives, 

 razors, scissors, chisels, iVcc. nails, pins, needles, 

 awls, &c., are ^vedges. The angle of the wedge, 

 in these cases, is more or le.ss acute, according 

 to the purpose to which it is to be applied. In 

 determining this, tsvo things are to be consid- 

 ered — the mechanical power, which is increas- 

 ed by diminishing the angle of the wedge, and 

 the strength of the tool, which is always dimin- 

 ished by the same cause. Thei*e is, therefore, a 

 practical limit to the increase of the po^ver. and 

 tliat degree of sharpness only is to be given to 

 the tool which is consistsnt with the strength 

 (609) 



requisite for the purpose to which it is to be ap- 

 plied. In tools intended for cuttmg \%ood, the 

 angle is generally about 30°. For iron, it is 

 from 50^ to 60^ , and for brass, from 80^ to 90^. 

 Tools which act by pressure may be made more 

 acute than tliose which are driven bj- a blow ; 

 and, in general, the softer and more yielding 

 the substance to be divided is, and the less the 

 po\ver required to act upon it, the more acute 

 the w-edge may be constructed. 



In many cases the utility of the wedge de- 

 pends on that w-hich is entirely omitted in its 

 tlieory, viz., the friction which arises bet\veen 

 its surface and the snbstance which it divides. 

 This is the case when pins, bolts, or nails, are 

 used for binding the parts of structures togeth- 

 er ; in -which case, were it not for the friction, 

 they would recoil fi-om their places, and fail to 

 produce tlie desired effect. Even when the 

 wedge is used as a mechanical engine, the pres- 

 ence of friction is absolutely indispensable to 

 its practical utility-. The power, as has afready 

 been stated, generallj" acts by successive blo\i-8, 

 and is tlierefore subject to constant intermission, 

 and, but for the friction, the -wedge would re- 

 coil between the intervals of the blows ^vith as 

 much force as it had been driven forward. — 

 Thus the object of tlie labor would be continu- 

 ally fnistrated. The friction, in this case, is of 

 the same use as a ratchet-wheel, but is much 

 more necessaiy, as the power applied to the 

 wedge is more liable to intermission tlian in the 

 cases where ratchet-wheels ai-e generally used. 



When a road directly ascends the side of a 

 hill, it is to be considered as an inclined plane ; 

 but it will not lose its mechanical character, if, 

 instead of directly ascending toward the top of 

 the hill, it winds successively round it, and 

 gradually ascends, so as, after several revolu- 

 tions, to "reach the top. In the same manner a 

 path may be conceived to surround a pillar, by 

 which the ascent may be facilitated upon the 

 principle of the inclined plane. Winding 

 stairs constructed in the interior of great col- 

 umns partake of this character: for although the 

 ascent be produced by successive steps, yet if a 

 floor could be made sufficientlj" rough to pre- 

 vent the feet fi-om slipping, the ascent \vould be 

 accomplished with equal facilit}-. In such a 

 case, the winding path would be equivalent to 

 an inclined plane, bent into such a form as to 

 accommodate it to tlie peculiar circumstances in 

 vi-hich it would be required to be used. It will 

 not be dilBcult to trace the resemblance be- 

 tween such an adaptation of the inclined plane 

 and the appearances presented by the thread 

 of a screic ; and it may hence be easily under- 

 stood that a screw is nothing more than an in- 

 clined plane constructed upon the smfaceofa 

 cylinder. 



This will perhaps be more apparent by the 



following contrivance: Let A B. fig. 6, be a 



common round ruler, and let C D E be a piece 



of white paper cut in the fonn of an inclined. 



Fig. 6. 



AC 



B 



F Q 



plane, whose hight C D is equal to the length 

 of the ruler A B, and let the edge C E of the pa- 

 per be marked with a broad black line : let the 



