PREFACE. 



'The house that is a-building looks not as the 

 house that is built.' The present Manual, though 

 now issued as complete, is, in truth, but the 

 abridgment of part of a larger work which the 

 Author trusts may yet one day see the light. 



The general arrangement of the subject-matter 

 here devised does not seem to require any expla- 

 nation. Had the Author sought to evade those 

 delays and difficulties with which, in almost every 

 paragraph, he has found it his duty to contend, 

 another, and far easier, plan might have been 

 chosen. A thoroughly scientific method seemed, 

 however, more likely to prove useful. And, in 

 the discussion of questions hitherto considered 

 unsusceptible of general treatment or, perhaps, 

 insufficiently known to men of science themselves, 

 he has not endeavoured, by the invention of diffi- 

 culties which in nature have no existence, to hide 

 truth beneath the patchwork veil of a meagre 

 quasi-originality. Rather has it been his wish to 



