tf AND r 



useful : the reader whose attention is called to this point will 

 have little difficulty in deciding the question for himself. We 

 merely give the general rule, that where dissections of plants 

 and animals are to be carried on, a simple microscope should 

 in general be chosen, while the compound microscope fur- 

 nished with good objectives, is indispensible whenever high 

 powers are required for the examination of objects. 



Having decided upon the kind of microscope that is needed, 

 the next step is to determine the individual quality of the dif- 

 ferent instruments that may be offered to us. To do this 

 thoroughly, it will in every case be found a good plan to take 

 up, point by point, all those elements that are necessary or desir- 

 able in a microscope, and in this way subject the instrument 

 to the most careful scrutiny. Unless a microscope is made 

 specially to order, it will be difficult to find one that will com- 

 bine all desirable features, but the plan we suggest certainly 

 enables us to decide most readily and accurately as to the pres- 

 ence or absence of those points which are desirable for our pur- 

 poses. The following are the chief points that demand atten- 

 tion: 



3Iagiiiyiug Power. We place this first, because usually 

 the first question in regard to a microscope that is asked by be- 

 ginners is, " What is its magnifying power? " Now magnifying 

 power, although an important element, is after all but a secondary 

 consideration. A microscope magnifying a thousand diame- 

 ters could easily be made and sold at a profit for five dollars, 

 and a few cents expended in paper and paste will at any time 

 double, or even treble, the magnifying power of an ordinary 

 compound instrument. The proper question is not how much 

 does a microscope magnify, but how much will it show. A 

 magnifying power of one hundred diameters, obtained by the 

 use of first-class objectives, will enable us to see more of the 

 true structure of an object than could be reached by a magni- 

 fying power of five hundred, the lenses in the latter case being 

 of inferior quality. But, although not the first consideration, 

 magnifying power is a feature of sufficient importance to deserve 

 careful deliberation, and without a knowledge of the powers 

 required, and the mode in which they are expressed, the begin- 



