PREFACE. 



xvii 



successful in his efforts, and obtain his full share 

 of the superior pleasure which scientific know- 

 ledge can so liberally bestow : he will find that 

 every onward step will render those which are 

 to follow less difficult ; and every increase of 

 knowledge thus gained, will be to him a new 

 source of delight, and a stimulating induce- 

 ment to proceed. 



