of fyt&t anfc €ofo* 6t 



this alfb might be heated , Chough 

 not fo foon nor fo much as the iron 5 ) 

 by which one may alfo take notice* 

 that 'tis not necefiary, a body fhould 

 be it felf hot, to be calorific* And 

 now I fpeak of (hiking an iron with 

 a Hamriier, I am put in mind of an 

 Obfervation that feems to contradift, 

 but does /Wee<^confirm,our Theory: 

 Namely, that , if A fomewhat large 

 nail be driven by a hammer into a 

 plank or piece of wood 5 it will re- 

 ceive divers ftrokes on the head be- 

 fore it grow hot 5 but when 'tis dri- 

 ven to the head, fo that it can go no 

 further^ a tew ftrokes will fuffice to 

 give it a confiderable Heat > for 

 whilfl, at every blow of the ham- 

 toer 3 the nail enters further and fur- 

 ther into the wood, the motion (that 

 is produced is chiefly progreffive^and 

 is of the whole nail tending one 

 way i whereas,, when that motion is 

 ftopt, then the imptilfe given by the 

 ftroke being unable either to dri^e 

 the nail further on, or deftroy its in* 

 tireneftj muft be (pent in making a 

 E 2 vari- 



