XX PREFACE. 



ferent departments of the work has been, as 

 nearly as possible, divided between them ; — that 

 though the letter, or series of letters, on any par- 

 ticular subject, has been usually undertaken by 

 one, some of the facts and illustrations have ge- 

 nerally been supplied by the other, and there are 

 a few to which they have jointly contributed;— 

 and that, throughout, the facts for which no 

 other authority is quoted, are to be considered as 

 resting- upon that of one or other of the authors, 

 but not always of him, who, from local allusions, 

 may be conceived the writer of the letter in which 

 they are introduced, as the matter furnished by 

 each to the letters of the other must necessarily 

 be given in the person of the supposed writer. 



In acknowledging their obligations to their 

 friends, the first place is due to Simon Wilkin, 

 Esq. of Costessey near Norwich, to whose libe- 

 rality they are indebted for the numerous plates 

 which illustrate and adorn the work ; the whole 

 of which have been drawn and engraved by 

 his artist Mr. John Curtis, whose intimate ac- 

 quaintance with the subject has enabled him to 

 give to the figures an accuracy which they could 

 not have received from one less conversant with 

 the science. Nor is the reader less under obliga- 

 tion to Mr. Wilkin's liberality than the authors. 



