OF THE MICROSCOPE. 93 



resembling the numbers assigned to objectives by continental 

 makers. A great improvement upon this arbitrary and uncer- 

 tain system would be to assign to each eye-piece its proper 

 power expressed in inches. Thus, an eye-piece magnifying the 

 same as a simple lens of two inches focus, should be called the 

 two-inch eye-piece. 



And here let us call attention to the terms deep and shallow, as 

 applied to eye-pieces. By all authors of repute, a deep eye- piece 

 is one of great magnifying power, while a shallow eye-piece ib the 

 reverse. See the Micrographic Dictionary, and the works of Car- 

 penter, Beale, Larduer, Frey, etc., etc. It is, therefore, singu- 

 lar that Dr. Lankester, in his popular little work, " Half-Hours 

 with the Microscope," should have committed the mistake of 

 giving definitions exactly the opposite, upon the ground 

 that eye-pieces of great magnifying power are always short, 

 while low eye-pieces are always long. It is evident, however, 

 that the terms are liable to give rise to confusion, and we pre- 

 fer the words high and low the meaning of which is so ob- 

 vious as to require no explanation, as every body knows what 

 high magnifying power is 



While clearness of definition and resolving power are the 

 most important qualities of every good microscope, magnifying 

 power is also of considerable consequence, as explained in a 

 former section. Therefore, every good microscope should be 

 provided with at least one eye-piece of considerable power. It 

 often happens that with the objectives and eye-pieces at hand, 

 the amplification, as it is called, or, in other words, the extent to 

 which the object is magnified, is not sufficiently great to enable 

 us to make out its structure, while the objective has not by 

 any means reached the limit of its defining power. In this 

 case a high power eye-piece, which costs comparatively little, 

 will greatly extend our power of successful examination. 



ACCESSOEY APPAKATUS. 



Every microscope should be accompanied with certain pieces 

 of accessory apparatus, which are necessary for the convenient 

 and thorough examination of objects, but which do not form 

 part of the instrument itself. Some of these are intended for 



