(4J> 

 lions by the help of fuch Theo- 

 ries. 



Bat before I had made any great 

 progrefs in the purfuit of this de- 

 fign, the fatal Peftilence that raged 

 in London^ and in many other parts of 

 England, in the years 1664 and 65, 

 obliging me among the reft to make 

 feyeral removes 5 which put me upon 

 taking new meafures, and engaging 

 me in other employments of my 

 time 3 made me fo long negled: the 

 Papers I had drawn up, that at laft I 

 knew not where to finde them 5 

 (though I hope they are not ytc 

 tniilaid beyond recovery,) which I 

 was the lefs troubled at, becaufe the 

 great difficulties, to be met with in 

 fuch an undertakings did not a little 

 difcourage me, fuch a Task requi- 

 ring as well as deferving a Perfoq 

 better furnifhed, than I had reafon 

 to think my felf, with Abilities, Lei- 

 fure 5 Chymical Experiments , and 

 Conveniences, to try as many more 

 as (hould appear needful. But yet 



to 



