SUPPLEMENT. 365 



seated convictions that the use of such lenses as I have de- 

 scribed will be of the greatest use in histological observations. 



Prof. Hitchcock's remarkable statement that *' much of the 

 very, best class of work is being done with second-class lenses," 

 is, I fear, a slip of the pen. I, for one, certainly cannot agree 

 with him, even if so be, that I am found in a " minority.' 7 



Prof. Hitchcock has, I fear, found out my weak side, and 

 punches me sorely with Helmholtz's formulas. He has got 

 things nicely tabulated, to show at a glance just what can be 

 done and what can't. ISTow, I own up that of all the annoying 

 things on this mundane sphere (to me), these confounded tables 

 take the lead. Years after others as well as myself, saw the 

 19th Nobert band as clearly as we saw anything, came the 

 tables to prove that the thing was an utter impossibility ! 

 It was noticeable too that, year after year, the tables got 

 changed, in fact, improved, to approximate more closely to the 

 facts. Verb. sap. 



Again, Mr. Hitchcock informs us that "to attain the best 

 possible results from an objective, the angle of the illuminating 

 pencil must be the same as the angular aperture of the objec- 

 tive." This, he says, is the u chosen ground " for any lens. 



To put it mildly, this is another most remarkable statement. 

 I dismiss it with the remark that my own experience teaches 

 me that such manipulation would defeat ninety low angled 

 glasses out of the hundred. He also, referring to my exhibition 

 of the 19th ]STobert band, with the vertical illuminator, sug- 

 gests the employment of a diaphragm to the back lens, pre- 

 dicting that the resolution would " doubtless be greatly 

 improved." I had already tried the experiment (and scores of 

 others); the result was nil. 



Prof. Hitchcock further says that " Prof. Smith has not 

 taught us anything new about objectives." Well, doubtless a 

 little setting back of this kind will be of benefit to me, and 

 may prevent the growth of undue conceit. I confess, that I 

 really did entertain the notion that some of my " shows " before 

 the Dunkirk Microscopical Society were novel. For instance, 

 the exhibition of the Nobert 19th band as an opaque object ; 

 ditto, the showing of 30,000 lines to the inch with an inch 

 objective, and under an amplification of 740 diameters, etc. 



