OP THE MICKOSCOPE. 171 



On the Use of Objectives of Large Apertures. 



When the first edition of tliis book was issued, wide-angled ob- 

 jectives were far from common. The "Battle of the Object- 

 Glasses " was at its height, and objectives capable of resolving 

 the Amphipleura pellucida, or Nobert's nineteenth band, by sim- 

 ple lamplight, were comparatively scarce. During the interven- 

 ing years the opticians have been hard at work, and have turned 

 out objectives of a high class to such an extent that almost 

 every microscopical society numbers amongst its members those 

 who have glasses of high balsam apertures. It is an unfortu- 

 nate fact, however, that thus far the text-books are entirely in- 

 nocent of any directions for using these glasses. We have now 

 before us a treatise of over 400 pages, which left the author's 

 hands as late as the middle of 1880, and which does not contain 

 a single direction for the use of the cover correction ! As a 

 justification of such omission, it has been alleged that objec- 

 tives of large aperture require no more care and skill than 

 others. From this position we most emphatically dissent, and 

 if evidence were wanting we could cite the case of a prominent 

 officer of one of our microscopical societies, and one who claims 

 to be an expert in the use of the microscope, who thought it a 

 great feat to show No. 18 of the Probe Platte with a objective, 

 which undoubtedly was capable of resolving No. 20 handsomely 

 if properly handled ! The forthcoming work of Prof. J. Ed- 

 wards Smith will probably be the first text-book that will have 

 treated this department thoroughly, and students are anxiously 

 looking forward to its appearance. 



Instruction in the proper methods of handling first-class 

 objectives is best obtained from a living teacher. It will be 

 found one of the most difficult things to learn from a book. 

 One reason for this is that until he has become expert, or has 

 seen the objects in the hands of some one who is expert, the 

 student does not know what appearance to look for. The con- 

 sequence is, that he is all the time working in the dark. But 

 after he has seen the Amphipleura or the Saxonica w.ell shown 

 by some one who knows how to handle a good objective, he 

 has a standard of excellence to go by, and it will be very strange 

 if, after a few trials, he does not surpass the work of his teacher. 

 Then, as soon as he has learned to bring out what he knows to 



