The Microscope. It 



ses/" Dr. Dallinger has here fallen into error. Bulloch's Gil- 

 lett diaphragm is bad, but not so bad as that. It cannot be 

 used above any condenser, and was never intended to be so 

 used, as the lamented optician himself informed the writer. 



Another criticism which, in the reviewer's opinion, may justly 

 be made, is in the sequence of the first three chapters. To be- 

 gin with the elementary principles of microscopical optics, as 

 the book does, passing to the second chapter on the principles 

 and theory of vision with the compound microscope, thence 

 leaping to the history and evolution of the microscope, and 

 thence, in chapter lY, to accessory apparatus, does not appear 

 to be a logfical arrano^ement. It would have been better to have 

 made chapter III (the history of the instrument) the first chap- 

 ter; chapter I (on elementary optics) the second, and chapter 

 II (the theory of microscopical vision) the third. These parts 

 should at least be read in this order. 



Dr. Dallinger in several instances uses the word ' microscopic ' 

 to describe the objective, referring to the " microscopic object- 

 ive " and to " microscopic vision," neither of which he means ; 

 indeed some objectives are not microscopic enough, some of 

 Tolles's, for instance, being unnecessarily macroscopic. The 

 editor also uses the far-fetched word " reflexion " in every 

 instance instead of the usual " reflection." It seems unneces- 

 sary to drag this old thing from its merited seclusion, and why 

 Dr. Dallinger should have done so is a mystery. At the first 

 meeting with it the reader is forced to pause to get the meaning, 

 while to meet it on almost every page soon becomes an annoy- 

 ance which, like the continuous pricking of a pin, finally grows 

 to o:yscure the horizon. But these and some similar points are 

 small defects in a book which is a monument to the editor's 

 learning, skill, patience and astonishing capability for hard work. 



ELEMENTARY MICROSCOPAL MOUNTING.— III. 



DR. A. M. WEBSTER, 

 CEMENTS. 



Although it is possible to mount an object with a slip, a cover 



glass and some resinous medium that shall surround the object 



and, after its volatile matter has evaporated, become hard, it is 



always well to use a cement in addition, either to form a cell or 



8 



