104 HOW TO SEE WITH THE MICROSCOPE. 



balsam angles to the tune of 100, or even higher. 

 In dealing with objectives of short focal distance, all 

 this may be well enough; the writer, however, prefers 

 to regard as high-angled, any, and all glasses, without 

 reference to their focal lengths, which are endowed 

 with the widest apertures obtainable. If this platform 

 be accepted, then it will occur that a one-inch of 50 

 should be classed as a high-angled objective, and simi- 

 larly, a two-inch of 25. And, again, it would also then 

 occur that a one-sixth of 130, which fifteen years ago 

 ranked as a wide, would now be classed as a glass of 

 medium aperture. And furthermore it may possibly 

 (yea probably} have place, that there are many observers 

 to-day, loud in their denunciations of the " wide-angles," 

 falling back on "The Microscope and its Revelations " 

 for authority, who, in their habitual use of what are 

 now known as medium apertures, are in truth the real 

 culprits, to whom and for whom were Dr. Carpenter's 

 original remarks intended. 



As has been suggested on a previous page, there may 

 be seriously some question, not only as to angular aper- 

 ture per se, but as to what constitutes the measure of 

 the same. It is one thing to get light through an ob- 

 jective, and quite another to bring said light into the 

 traces, and render it of use to the observer. There are, 

 too, scores of high-angled glasses (so-called) sold as 

 having angle of 175, and possibly more, that are 

 entirely worthless when worked with pencils beyond 

 130 ; indeed, many that I have seen would utterly fail 

 when compared with a really good glass of 115. 



