212 HOW TO SEE WITH THE MICROSCOPE. 



to keep well " an eye to windward." And it may be 

 here we can render quasi assistance, thus : 



Judging the future from the past, it seems more than 

 likely that our opticians will at no distant day produce 

 one-fourth, one-fifth or one-sixth quite equal in every 

 respect to the one-tenth of to-day, and possibly with a 

 greater working distance. The author, within the last 

 twenty-four hours, has received reliable testimony af- 

 firming that young Spencer has succeeded in making a 

 wet and dry one-sixth fully up to the performance of 

 the one-tenth, of which mention has before been made 

 in these pages. This one-sixth we have not seen, but 

 are informed that it is now in the hands of an eminent 

 microscopist, who will exhibit it at the Paris expos- 

 ition. 



Again it may be possible that the optician will suc- 

 ceed in enlarging the aperture of the low powers. 

 Heretofore 45 has been regarded as the limit of anofle 



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for the inch; with our present knowledge it appears 

 almost an impossibility to extend the present limit much 

 beyond the figure named, unless, indeed, the calibre of 

 the objective be increased. It will be advisable, never- 

 theless, to bear in mind that in the late march of ad- 

 vancement of the American objective, several desirable 

 points, formerly declared " impossible" have been mas- 

 tered by the optician, and are to-day " un fait accompli.'" 

 Now if it shall be so that the optician succeed in pro- 

 ducing a one-fourth equaling in angle and performance 

 the present work of the one-tenth, or that the one-inch 

 shall in the future rival the work of the two-thirds of 



