X PREFACE. 



At any rate, the Author's constant object and 

 desire has been thus to present them; it will be 

 for the reader to judge how far he has succeeded 

 in this design. 



But inasmuch as nothing is ever done in Nature 

 without some definite object, and in pursuance 

 of a regular system of law; the Author has con- 

 stantly endeavoured, throughout these volumes to 

 interpret, as far as he has been able, what have 

 seemed to him to be the causes of the various 

 phenomena which have been described. In doing 

 so, however, as the reader will see, the student 

 of Nature is brought face to face in almost every 

 instance, with a series of details, involving the 

 consideration of one or more questions of scientific 

 enquiry. The individual man might therefore well 

 stand appalled at the wide extent of research, 

 which even a very partial attempt to deal success- 

 fully with all these topics, is sure to cast upon 

 him. The Author has been painfully impressed 

 with this fact, but that has not seemed to him 

 to be a reason which ought to cause him to 

 hesitate to do his best in this direction. 



Of course it would be impossible to suppose 

 that a work involving so great a variety of technical 

 matters as are here attempted to be dealt with, 

 would not be defaced by many errors and short- 

 comings ; all that the Author has a right to expect, 

 however, is, that under the circumstances, his readers 

 will make due allowance for the difficulties of the 

 task which he has attempted to perform ; and he is 

 sure that he will not appeal in vain to the British 

 Public, for their kindly consideration in this case. 



