PREFACE. Xlll 



subject, and in order to avoid tedious and 

 fatiguing circumlocution, to employ many 

 terms of science, I have been careful to ex- 

 plain the meaning of each when first intro- 

 duced : but as it might frequently happen that, 

 on a subsequent occurrence, their signification 

 may have been forgotten, the reader will 

 generally find in the index, which I have, 

 with this view, made very copious, a reference 

 to the passage where the term is explained. 



I beg, in this place, to express my deep 

 sense of the obligation conferred on me by 

 Mr. Davies Gilbert, the late president of the 

 Royal Society, to whose kindness I owe my 

 being appointed to write this treatise. 



I also take this opportunity of conveying 

 my best thanks to my friend and colleague, 

 Mr. Children, of the British Museum, for his 

 kind assistance in revising the sheets while 

 the work was printing, and for his many valu- 

 able suggestions during its progress through 

 the press. 



A catalogue of the wood engravings has 

 been subjoined ; and also a tabular view of the 



