OP THE MICROSCOPE. 91 



scope, a large part of this sum should be laid out in the pur- 

 chase of objectives of the better class, the one-inch and one- 

 fourth, or the three-fourths and one-fifth being those that are 

 usually selected by beginners. 



French triplets are, however, going rapidly out of use, from 

 the fortunate circumstance that objectives of low price and 

 excellent quality are now produced by several makers of repute. 

 It is well, however, for the reader to be on his guard against 

 a fraud which has been but too common of late years. Some 

 so-called opticians go so far as to add a little brass- work and 

 engraving, and sell these French triplets as objectives of Ameri- 

 can make. We do not here refer to the mere operation of attach- 

 ing the objective to an adapter, and fitting it in a brass box, for 

 this adds greatly to the convenience with which such minute 

 objectives may be handled and preserved, but to a sort of 

 "making over," by which they are completely disguised and 

 made to resemble the objectives of English and American 

 makers. It is hardly necessary to characterize such a pro- 

 ceeding. 



Eye-Pieces. The eye-piece that is at present almost uni- 

 versally used is the Huyghenian, which, when well made, gives 

 very excellent results. In the use of low powers, wheie a very 

 flat and large field is desirable, the Huyghenian eye-piece fails, 

 and the same is also true in regard to very high magnifying 

 powers, where the enlargement is obtained in a great measure 

 by means of the eye-piece. The extent to which the definition 

 of really good objectives is deteriorated by the use of eye-pieces 

 of great magnifying power, and the loss of light which they 

 occasion, render them practically useless. For high powers, 

 the solid eye-pieces of Mr. Tolles are vastly superior, while for 

 low powers, where a large flat field is desired, Kelner's ortho- 

 scopic eye-piece presents important advantages. 



Mr. Gundlach has recently brought out a new eye-piece, 

 which he has named the periscopic, and for which a large field 

 and excellent definition are claimed. They are much more ex- 

 pensive than the Huyghenian. We have not had an oppor- 

 tunity of examining them carefully. 



In determining the quality of an eye-piece, attention is to be 



