iv OPTICAL PROJECTION 



work treating Physical Optics from this point of view, 

 ample evidence has been furnished that others have felt 

 strongly the same fascination as myself in this class of 

 experiments. 



The preparation of the following pages, as a treatise 

 upon the more general use and manipulation of the 

 Lantern through its entire range, in a manner that may 

 suggest proper arrangements even where want of space 

 or my own lack of detailed experience may prevent specific 

 treatment, was not spontaneous on my part, but waa 

 suggested to me by Mr. Herbert C. Newton. During 

 years past I have spent very many hours associated 

 with him many of them actually in his company- 

 engaged in contriving, perfecting, testing, or adjusting 

 scientific optical apparatus ; often for myself, but more 

 frequently for the use of others, and especially of 

 colleges and public institutions. He was good enough 

 to suggest on many occasions that a practical treatise 

 from my pen, and embodying the results of my experience, 

 would be of service ; in fact he has urged the task upon 

 me with some persistence. Whether or not I have been 

 able to add anything of value to such handbooks as were 

 previously obtainable, must be left to the reader's judg- 

 ment. But that is the real origin of this work; and 

 it is best to state it frankly, because it will naturally 

 account for such description as will be found hereafter 

 of apparatus microscopic and polariscopic in particular 

 which was worked out to the best of my ability with 

 a primary view to being constructed by the firm which 

 Mr. Newton represents, from whom I have received 



