body it afts Upon, As when Goldfmiths 

 burnifh a Plate or Veffel of Silver, that ha- 

 ving been lately boird lookt white before, 

 though they deprive it of the greateft 

 part of its colour, and give it a new power 

 of reflecting the beams of Light and vi- 

 fible Objcdts, in the manner proper to 

 fpecular bodies > yet all this is done by 

 the intervention of a burnifhing Tool, 

 which often is but a piece of Steel or Iron 

 conveniently fhap'd ; and all that this 

 Burniftier does , is but to depre fsthelit- 

 tie prominencies of the Silver, and reduce 

 them, and the little cavites of it, to one 

 phyfically level or plain Superficies. And 

 fo when a Hammer ftriking often on a 

 Nail, makes t^e head of it grow hot, the 

 Hammer is but a purely Mechanical A- 

 gent , and works by local motion. And 

 when by ftriking a lump of Glafs, it breaks 

 it into a multitude of fmall parts that 

 compofe a white powder, it a£tsas Me- 

 chanically in the produd^ion of that 

 Whitenefs as it does in dr ving in a Nail 

 to the head. And folikewife, when the 

 powderM Glafs or Colophony lately men- 

 tion'd is , by the fire, from a white and 

 opacous body , redue'd into a colourlefs 

 ( or a reddifh ) and tranfparent one , it 

 appears not, that the fire* though a na- 

 tural Agent, need work ctherwft than 



Mecha- 



