PREFACE. 
lent kind of knowledge, and worthy of our 
purfuit; and if all thofe works, though diffe¬ 
rent in degrees of fplendor, are dill perfedj 
it is hoped, that an humble attempt to im¬ 
prove, and encourage the dudy of any branch 
of Natural Philofophy, will not be unaccep¬ 
table to the public. And fmce the knowledge 
of the microfcope has always been looked upon 
as no inconfiderable branch of Natural Philo¬ 
fophy, and as that part of it has particularly 
fallen within the compafs of my dudies, I 
have made it the fubjed of the following trea- 
tifej a fubjed, which has fo often employed 
the mod learned men, that it can hardly dand 
in need of an apology for the choice of it. 
In this edition is given a defcription of feve- 
ral new and valuable difcoveries. 
I. The new variable microfcope, which is 
both dngle and compound. 
II. A benedcial improvement of the folar 
microfcope, in which we have fucceeded beyond 
expedation. By this acquifition, we have now 
an opportunity of examining all microfcopic 
objeds, either in the fun-fhine, or at night in 
winter evenings. 
III. A 
