F R E F A C E. 



In the third chapter, the mod improved microfcopes, and Tome 

 others which are in general ufe, are particularly defcribed; no 

 pains have been fpared to leffen the difficulty of obfervation, and 

 remove obfcurity from defcription ; the relative advantages of 

 each inftrument are briefly pointed out, to enabfe the reader to 

 felecl that which is bell adapted to his purfuits. The method of 

 preparing different objects for obfervation,. and the cautions 

 neceflary to be obferved in the ufe of the microfcope, are the 

 fubject of the fourth chapter. 



When I undertook the prefent efTays, I had confined my- 

 felftoa re-publication of my father's work, entitled, Microgra- 

 phia Illuftrata ; but I foon found that both his and Mr. Baker's, 

 tracts on the microfcope were very imperfect. Natural hiftory 

 had not been fo much cultivated at the period when they wrote 

 as it is in the prefent day. To the want of that information 

 which is now eafily obtained, we may, with propriety, impute 

 their errors and imperfections. I have endeavoured to remedy 

 their defects, by arranging the fubjects in fyftematic order, and 

 by introducing the microfcopic reader to the fyftem of Linnseus, 

 as far as relates to infects : by this he will learn to difcriminate 

 one infect from another, to characterize their different parts, and 

 thus be better enabled to convey inRruction to others, and to* 

 avoid error hjmfelf 



As the transformations which infects undergo, eonftitute a prin- 

 cipal branch of their hiftory, and furnifh many objects for 

 the microfcope, I have given a very ample defcription of them; 

 the more fo, as many microfcopic writers, by not confidering 

 fchefe changes with attention^ have fallen.into a variety of miftakes. 



