400 HOW TO SEE WITH THE MICROSCOPE. 



made with angles sufficiently high to injure penetration." Here 

 is involved an error in fact, one quite pardonable too. Not Jong 

 since a German gentleman remarked to the writer that it seemed 

 to him that when the London opticians demonstrated a certain 

 opticial law, some Yankee optician would be just mean enough 

 to make an objective that would upset the whole arrangementl 

 And it is perforce of this /ac that Mr. Lapham becomes involved 

 in his very pardonable error. Now I have in my possession a 

 two- thirds of the Messrs. Spencers of 48 aperture. They have 

 lately made to my order an inch of 47. The clear diameter of 

 both glasses is about the same; the working distance of the 

 two-thirds is 25-100ths of an inch, while that of the inch is but 

 13-100ths of an inch, arid the " penetration" of the latter (so- 

 called) is less than that of the 2-3ds. In fact the penetration of 

 the inch is "injured," as compared with one of 30. The reader 

 will notice that Mr. Wenham's pet theory gets also into grief. 

 I assure Mr. Lapham that this new inch is a glorious glass, pene- 

 tration or no penetration. 



Finally, I desire to extend to Mr. Lapham personally my 

 thanks for his instructive and interesting article. It will be a 

 pleasure, and, I doubt not, profit to compare notes with him r 

 and, in the words of my very generous opponent, Prof Hitch- 

 cock, I will add that all I desire is ''the facts." Mr. Lapham T 

 by the way, will be pretty sure to catch it, about that 180, from 

 Prof. II., on the u impossible" and the tw absurd." 



It may be well enough to add that my first impulse was to 

 write Mr. Lapham privately for an interchange of personal 

 experiences, but on reflection chose this, the more public plan, 

 hoping to enlist the attention of others in the same direction. 



OLEOMARGARINE AGAIN. 



Ed. Am. Jour. Microscopy: The article giving " The Micro- 

 scopical Examinations of Oleomargarine," by Prof. Michels, 

 which appeared in a recent issue of this journal, was perused 

 by me with much interest, and I at once resolved to repeat the 

 experiments as detailed. 



The first thing requisite was to secure authentic specimens of 



