428 Dr. Goring on Achromatic Microscopes* 



ordinary objects is given. I need scarce say that figs, 5 and 

 6, and the whole of that stubborn and indomitable race to 

 which they belong, utterly resist the penetration of the single 

 solar achromatics. As to the amplifying power necessary 

 to demonstrate the lines on the feathers, I may state that 

 figs. 1 and 7 begin to be barely visible in a very perfect in- 

 strument and with very close attention^ with a degree equal 

 only to that of a lens of } of an inch focus ; but figs. 5 and 6 

 require one equal to -J--^ of an inch at least. 



Fiff. 8. J^'^g' 8 is a drawing of the point 



of a leaf of hedge moss (I am sorry 

 I am at a loss how to designate it 

 scientifically) : it is a very good test 

 object, requiring a considerable an- 

 gle of aperture combined with great 

 distinctness fully to develope the 

 lozenges which constitute its fabric, 

 making out a luminous nucleus to 

 each, which should be sharply de- 

 fined and of the same shape with 

 the outer lozenge, and not melting 

 into it by insensible gradation as in the copperplate engraving. 

 The Amician microscope is sure to boggle at this subject, if 

 the figures of the metals are not good. All mosses exhibit 

 more or less of this structure ; but the specimen in question is 

 remarkable for the prominence of its features. The engrav- 

 ing being very exact, except in the trifling circumstance I 

 have mentioned, any specimen tried and not found to re- 

 semble it must be set down as another sort : the wood-cut in 

 the margin is correct. 



Fig. 9. Fig. 9. Bat's hair. — The hair of the bat near its 

 insertion in the skin often shows an outline similar to 

 that in the plate, being apparently the result of a 

 certain spiral coil wound about it : frequently, how- 

 ever, it shows an appearance similar to that produced 

 by the insertion of a number of funnels into each 

 other. When well defined as a transparent object by a 

 microscope of large aperture, it is a sure test of its distinct- 

 ness. I have given it as an opaque object, in which way it 

 is far more difficult of vision than as a diaphonous one. The 



