122 HOW TO SEE WITH THE MICROSCOPE. 



those who have not, may reasonably be expected to- 

 know not. 



Let it be required to display an object under the 

 microscope, and under a given amplification. It 

 matters not what the object may be be it a diatom, or 

 a bit of voluntary muscle, or what not; nor dees it 

 matter as to the amplification be it 60, 600, or 6000' 

 diameters, as the case may be. 



Now, to attack this object, we will provide two sets- 

 of objectives, including all the focal lengths, say from 

 the inch, upwards, to the one-fiftieth these glasses to- 

 be the very finest of their kind made at the present day, 

 and notably of low apertures ; the other set to be simi- 

 lar -as to the range of focal length and quality, but 

 notably to possess the highest apertures (respectively) 

 known. 



Now choose your object, select your amplification,, 

 and display the former, using the low angles with their 

 very best foot foremost. This done, allow me to- 

 remove the objective, replacing in its stead the suitable 

 high-angled glass, and I affirm pointedly that the object 

 shall be equally well displayed, under the same amplifi- 

 cation, etc., and by an objective, too, having greater 

 working distance than the low angle first selected. 



It should be contemplated, in any competitive com- 

 parisons of this kind, that they be conducted without 

 prejudice, and solely in the interests of science, and 

 when so conducted, and by observers fitted for the 

 emergency, the author apprehends that his statements 

 will be found correct. 



