30 METHODS OF MICROSCOPICAL RESEARCH. 



when the monocular instrument is exchanged for 

 the binocular it is often found that the eyes have 

 ceased to be a pair, and do not see alike. 



Two eyepieces should be available with the work- 

 ing microscope, the ordinary, or A, and a thoroughly 

 good C eyepiece, and two objectives. After thirty 

 years of constant work the author advises that these 

 two powers should be a first rate 1-g- and a J inch. 

 These, with the two eyepieces, will give a series of 

 four magnifications and prove amply sufficient for 

 all ordinary work, and the objectives can be con- 

 veniently used with a double nose-piece, except 

 when dissecting or other such work is being done 

 under the microscope and the nose-piece shall be 

 found to interfere with free manipulation. It is 

 well to take care that the objectives are as nearly 

 as possible of the same length, in order to avoid the 

 risk of breaking the slide under the microscope a 

 catastrophe very likely to occur either from momen- 

 tary forgetfulness of which power may be in use, 

 or hurry in changing the objectives. There is no 

 difficulty in obtaining a 1^ and J inch objectives so 

 arranged as to require but little alteration of the 

 rackwork of the microscope to focus them alter- 

 nately. Whilst a 1-g- inch objective will be found 

 the most useful of all glasses for ordinary work 

 and for most purposes, it will often be found neces- 

 sary in the course of the work to make examinations 

 of its parts and progress by means of the J inch. 

 With English microscopes it is advisable, as a rule, 

 to use English objectives, but admirable glasses of 

 great penetrating power and definition by foreign 

 makers can now be obtained at a much less cost 

 than those of English manufacture. The object- 



