24 THE MICROSCOPE 



inch, we know that the object is magnified ten times ; if only four 

 of these lines occupy an inch, the object is magnified twenty-five 

 times, and so on. But this method of drawing objects from the 

 microscope may not be applicable for all users of the microscope, 

 and those who are unable to adopt it will do well to purchase a 

 camera lucida, or, if expense be an item of consideration, one of 

 the many forms of neutral-tint reflectors will be found to meet 

 every requirement. 



We will now describe more particularly some of the principal 

 accessories : — 



The Object-glasses possess various magnifying powers, accord- 

 ing to the distance at which they require to be placed from the 

 object for distinct vision. This, though not absolutely correct, 

 yet may serve as a general expression. Thus, we have i-inch, 

 J-inch, ^-inch, ^-inch, 25-inch object-glasses, etc. As the coarse 

 movement raises or depresses the body and object-glass through 

 comparatively large distances, it must be used only on the lower- 

 power object-glasses, as the 2-inch, i-inch, or ^-inch, or, to bring 

 the object-glass near the focal distance with the higher powers, as 

 the ^-inch, etc. Care should also be taken not to place a slide 

 which has been warmed in any experiment near the object-glass 

 until it has become quite cold. 



Eye-pieces. — With all microscopes, one, two, or more eye- 

 pieces are supplied. These possess different magnifying powers, 

 and are lettered or numbered accordingly, the lowest powers with 

 the earliest letters of the alphabet, or with the smallest numbers ; 

 thus, A, B, C, or i, 2, 3, etc. 



The following instruments are required for general work ; of 

 course, the list does not include all, but others may be added at 

 the convenience of the student, and those students who make 

 histology their special subject will naturally require many more. 



Stage-forceps for holding insects and small objects under the 

 microscope; straight and curved forceps for general manipulation; 

 live-box for holding living insects whilst under examination ; a pair 

 of straight and a pair of curved-bladed scissors ; a few mounted 

 needles for " teasing " out structural details ; a set of dipping 

 tubes ; a razor or two ; and an ether freezing microtome, 

 or a small hand microtome for those whose means are 



