No. 151.] 187 



All cams, when formed, are connected with their fellow levers by 

 cam-pins working into their grooves, or otherwise yoked to, or ap- 

 plied against them, to give alternating or vibrating motions to the 

 same. 



A prominent feature in cams proper, is that they have an inde- 

 pendent continuous movement in their action, from which primary 

 motions are derived independent of second causes, excepting the driv- 

 ing power communicated through their axles. 



Other mechanical devices, acting similarly, but not possessing this 

 continuous quality, are merely auxiliary means within the range of 

 mechanical contrivance, to effect required motions, to which no gene- 

 ral appellation or name can be given. 



We will notice two modes of acquiring motion, well known to 

 mechanics, to illustrate the point in question. 



First. — To a body moving in a circular or straight line, we at- 

 tach a lever by a pivot pin; place parallel therewith a stationary 

 piece, having a groove" formed in the face of it, deviating from such 

 circuit or plane of the moving body; connect such groove and the 

 end of such lever together by a pin working in the groove, and va- 

 ried and compound motion will be given to such lever, by the action 

 of such body and the deviating course of the groove in the stationa- 

 ry piece — the action of which will resemble and be of the character 

 and effect of a cam; but acting from borrowed motion only, is se- 

 condary in its character, and can only be denominated a stationary 

 guide-piece to the lever, and therefore is not a cam. 



Se:ond. — Forn\ a groove, deviating more or less from the plane of 

 motion of a body which moves in a straight line, or through the 

 section of a circle, but reciprocating back and forward ; connect 

 therewith, by a pivot pin working in the groove, a vibrating lever 

 whose centre is stationary; upon motion being given to such body, 

 in the manner named, vibrations are effected upon the lever, and pro- 

 duce such motions as are indicated by th,e formation of the groove, 

 and partake in some respects of the qualities of cam motions, but 

 being borrowed and secondary, possess no distinctive trait, by which 

 to give such body a proper name, and are in all respects like the 

 first described, only reversed; that is, they are moving guide-pieces 

 to stationary leveis, instead of stationary guide-pieces to moving 

 levers; the first being compound, and the second simply in action. 



