VI PREFACE. 



quentiy finds it more and more difficult to acquire such a 

 grasp of the whole subject as is requisite to enable him to 

 give a scientific description of it. 



It was with feelings of this kind that I undertook the 

 Editorship of the present collection ; and the willing co-opera- 

 tion I have obtained from the best workers of the day, on the 

 one hand, and the liberality of the publishers on the other, have 

 enabled me to bring it to a happy conclusion. 



A review of the whole work, however, compels me to admit 

 that it does not present the same uniformity that it would 

 otherwise have done had it been the outcome of a single master 

 mind. Some pages glow with the results of the long-continued 

 industry of the best investigators of our time, and sometimes 

 again these nodal points, so to speak, appear joined together 

 by the labour of younger hands. It lacks, however, that white- 

 wash with which our master builders, following the usual 

 custom, are wont to cover their constructions in order to hide 

 from the eye of the observer all the piece-work of their men 

 the good bits equally with the bad. 



My collaborateurs will, however, suffer no detriment by 

 aiding in the construction of this fabric, how rude soever it 

 may be. The more experienced and advanced certainly not, 

 for light is never darkened by a less light, whilst the younger . 

 ones will assuredly not complain that their participation is 

 manifest. 



It can only then remain a question whether the reader, and 

 above all, whether Science, has gained anything by this pro- 

 ceeding. The two questions are really reducible to one ; for the 

 interests of the reader cannot be better promoted than by 

 presenting to him whatever best responds to the demands of 

 the advance of Science. 



It requires no further argument to prove that the true 

 features are better seen in proportion as the use of paint is 

 avoided. 



