372 HOW TO SEE WITH THE MICROSCOPE. 



To get back to our " moutons." When I stated 30,000 as the 

 limit for definition of the inch, I held a good large margin (to 

 swear by) in reserve. This, as the 30,000 was " millions " as far 

 as establishing my point was concerned, now that the readers of 

 this journal have got used to the ' SO " I will add that I have no 

 trouble in seeing the 40,000 band of a Rodger's test-plate, and 

 most beautifully ruled they are. Here is an added strain of ten 

 thousand on the inch, but it is as good as ever ! (One of these 

 days I must give your readers a description of an exquisitely 

 ruled plate, up to 80,000 to the inch, and by the same talented 

 artist. ) 



But to business. I have as fine a half-inch of 38 as I have 

 ever seen, a glass selected with much care, having spent consid- 

 erable time in making the selection, so as to have the very best; 

 for, be it known, I sometimes (not often) have use for just this 

 sort of glass. Well, now, this half-inch has shorter working 

 distance, and, as a matter of course, less penetration than has 

 the inch of 45, while the last-named inch of 45 has much the 

 superior definition. 



Now, I am perfectly acquainted with the '* points " of these 

 two objectives, and can make either put its " best foot fore- 

 most," (hence the " handling " may be counted out.) Both are 

 my own, and I can at will use th3 one that I prefer. Which 

 would Prof. Hitchcock use under the same circumstances ? Or, 

 leaving the Professor out, which would the reader select ? 

 Which glass would be " strained " the most ? 



Prof. Hitchcock reminds his readers that he has " already ad- 

 mitted to Prof. Smith that Tolles and Spencer are making won- 

 derful glasses, etc." Yes, so he did, but he put a fence round 

 them ; thus he adds " but for resolutions only." When Prof. 

 Hitchcock shall become as well acquainted with the work of 

 Spencer and Tolles as are others, that fence will step down and 

 out. I accept no loop-hole, but stand to the position heretofore 

 assumed, to-wit, that the above named glasses are not equalled 

 for il any and all work," a* set forth in my last paper. 



Now about Dr. Johnson's showing the 19th band as an opaque 

 object in the year 1872 or thereabouts. Here is a legitimate 

 chance to try on Prof. Hitchcock's conditions, to-wit: Were 



