PREFACE v 



much kindness and assiduous care in my own personal 

 requirements of this kind. Such apparatus, to express 

 it briefly, is described here not as their apparatus, but 

 as being in greater or less degree my apparatus, by 

 contrivance, or selection, or modification, or personal 

 connection with it in some way or other, even when not 

 (as frequently the case) planned in the first instance for 

 my own use. , 



But while it is best to state this quite simply, it will 

 I trust be found that, beyond what thus became 

 unavoidable as forming part of that very experience 

 which is the basis of the whole, the subject has been 

 treated so as to be of most use to all, and without 

 any prejudice to other optical workshops of well-known 

 character with which I do not happen to have been 

 brought into the same personal contact. Except a very 

 few articles or details which may be patented in various 

 quarters, and which are well known to the trade and 

 readily obtainable from the various manufacturers, the 

 apparatus and arrangements here described are free to 

 all. It is perfectly open to any reader to have them 

 constructed by whom he chooses, with any improvements 

 he can suggest ; while it is equally open to any optician 

 to construct them as excellently, and sell them as 

 cheaply or the other way if he prefers as he possibly 

 can. 



I need only add to this explanation, that in the 

 following pages the first person singular has been pur- 

 posely adopted, as more simple and less really egotistic in 

 a book of such necessarily strong individuality, than any 



