64 The Advancing Powers of Microscopic Definition. 



At the time of penning these lines these specimens have not 

 been as yet seen by the writer. 



The acumen of the Chevaher in microscopic research is well 

 evidenced by his telling remark that he has proved the real nature 

 of the Surirella gemma (so beautifully photographed by Colonel 

 Woodward), " that most beautiful puzzle," for he says " I have seen 

 the dots which this interesting diatom wears. This appearance 

 must be the true one, because, having tried that same diatom with 

 a double reflector obliquely disposed at right angles to each other, 

 I have obtained the same appearances." It is worth recounting 

 that the Chevalier used immersion objectives of Koss ^V and Nos. 9 

 and 11 of Hartnack, and that* Mr. Mclntire employed a Hartnack 

 also, which he exhibited to me at my residence about two years ago. 

 The improvements, however, which have been made by Messrs. 

 Powell and Lealand in their objectives, have given a new impulse to 

 minute investigation, and I can speak highly of a new one-fiftieth 

 of an inch immersion objective, expressly constructed for me — the 

 first they have made upon their newly-discovered principles of con- 

 struction. And this exquisite glass has been employed by me to 

 re-test some of the more remarkable results previously obtained. 



Thus, in viewing the fringes of delicate objects, I have observed a 

 better defined outline, the most difficult of all kinds of pure and un- 

 alloyed definition. The serrated edges and quill-like projections of 

 the ribs of scales have been more sharply, clearly, and more distinctly 

 cut in a light and dark tracery. 



I have also observed the general beading of a variety of scales 

 hitherto totally " impalpable " wnth ordinary glasses employed in 

 the usual manner. Just as twenty-five years ago ordinary glasses 

 only gave a lined appearance to the then difficult tests, such as the 

 Navicula hi])]pocam.pus, and just as an ordinary |^th now only gives 

 the delicate longitudinal ribs on the scales detached from the gnat's 

 wing, which indeed generally presents a pale structureless smooth 



is obtained, the most beautiful appearance of double- striated beading I have yet been 

 able to observe : judging from a comparison with the beading of the Rhomboides, 

 I should estimate them at 100,000 (one hundred thousand) per inch. They can be 

 readily counted in close contact at the serrated end of the scale. The lines on 

 Nobert's 19th band appear to be about ^^u^th in diameter. The Rhetenor bead- 

 ing can be distinguished with an old but excellent quarter, or rather fifth of 

 Andrew Ross, 1851 date. 



The " Atlas, China," is a magnificent object at 4000 diameters with Powell and 

 Lealand's new -|^th immension. 



The Deilephda Klpenor is a beaded but accurately-striated scale, so regular as to 

 appear absolutely perfect, and presenting the most delicate molecular structure 

 imaginable. 



Many of the scales sent by tlie Chevalier Huyttens de Cerbecq are formed of 

 longitudinal striated be;iding, crossed with short double rows of transverse bead- 

 ing, containing about four or five beads in each transverse bar, but much smaller 

 than the longitudinal of which the Deilephila is a most interesting type. 



