ee eee

ON THE PLOUGH. 47

vary confiderably according to circumftan- ces.

Could this center be accurately found, a plough might be conftructed at once, that would perform its work perfe@ly, without further alteration; and there would be no neceflity to leave the principal parts in a ftate moveable by wedges to obtain their true pofition. In working, however, this center may be very nearly determined; be- caufe it will always be found in the line of direétion of the force produced downward from the point of the beam; and we may be affured this line pafles through the center, when it exactly balances the inclination of the coulter. But, before application to ufe, the fituation of the center can only be guef- fed at, which, indeed, by the aid of experi- ence in fimilar cafes, may be done with a good deal of accuracy; at leaft, fo accurately, that a{mall alteration in the pofition of the beam, which is left practicable on purpofe, will remove the bad effect of any error that may be committed in the conftruction.

This center will commonly be found a few inches above the middle of the fhare, though,