PREFACE. 11 



with earnest opposition from my readers. A large cor- 

 respondence ensued, while many microscopists visited 

 me for the purpose of witnessing, by way of ocular 

 demonstrations, the performance of the duplex glasses. 



Meanwhile, in London, England, a lively controversy, 

 known in microscope circles as " the war of the aper- 

 tures," appeared in the columns of the London Monthly 

 Journal of Microscopy, in which controversy the posi- 

 tions assumed by Mr. Tolles were assailed by Mr. F. A. 

 Wenham. The issues involved, however, appertained 

 only to optical possibilities, the performance of the du- 

 plex objectives being an entirely outside matter. During 

 the London battle Mr. Tolles was ably assisted by Dr. 

 J. J. Woodward, of Washington, D. C., and by Prof. 

 Keith of Georgetown. Suffice it here to say, that frorr 

 the standpoint of optical science Mr. Tolles maintainet 

 his positions, a fact, I believe, now generally admitted, 



And now, after a period of nearly six years, it is to 

 me a matter of pride to here record that of the several 

 11 heterodox" positions I had assumed in public print, 

 there has occurred, neither in the interim, or at this 

 present writing, no occasion to retract one word of what 

 was claimed by me in my former contributions to the 

 Cincinnati Medical Ifeivs. The duplex objectives have 

 steadily, and perforce of intrinsic worth, forced their 

 way into general use, while the leading opticians are 

 exerting themselves to still further improve their 

 performance. 



Having, as I have above briefly set forth, had a very 

 large experience with the four-system objectives, it was 



