AND MODERN MICROSCOPES. 99 
With Tolles 4 immersion, angular aperture 170°, B eye- 
piece, power 550, Mr. Greenleaf and myself both saw the 
19th band satisfactorily. Thus being probably the first ever 
to see lines of 112,000 to the inch, and establishing the fact 
of the visibility of such lines, contrary to the theory of the 
physicists. (It should, however, have been mentioned in * 
the proper place that Mr. Eulenstien says that Nachet claims 
to have seen them by sunlight recently, which claim needs 
some confirmation, as his No. 10 failed so completely in my 
hands. 
In the present month (January, 1868), Dr. F. A. P. Barnard 
writes to Mr. Greenleaf, that he had tried several objectives, 
naming a Spencer 34 and zy, a Tolles’ 4 and 4, a Wales }, 
and a Nachet immersion No. 8, equal toa 74. “The Spencer 
z, and the Natchet 4 broke down at about the 11th or 12th 
band. With the Wales 4 I got as far as ten, or perhaps 
eleven bands. With the Tolles’ 4 I made out distinctly ten.” 
In another communication he says, “the highest band I 
can count is the 16th.” In a more recent letter to the 
writer, Dr. Barnard gives the count of the lines on a portion 
of his plate, —corresponding as nearly as could be expected 
to figures given in the table up to the 14th; but the 16th 
band he could not count satisfactorily, different attempts 
giving varying results. It has been said that the resolution 
of the lines to the eye implies the ability to count them, 
but this I think is a fallacy ; a few lines of a group may be 
counted correctly, and then it becomes difficult to identify 
the line last counted and the one to be counted next. Let 
any one try to count the pickets in a fence, when the pickets 
are distinctly visible, say at a distance of 100, or 150 yards, 



Nachet’s immersion No. 10 = 1-21, B eye-piece, sunlight obliqu i 12th band. 
Tolles’ immersion 1-10, ang. ap. about 160°, B eye-piece, aara abou t 800, 
wunlinht ooteal o i a Oe ee i BOE RE Eee 
Tolles’ immersion 1-10, ang. ap. about 160°, B eye-piece, power about 800, 
sunlight o oblique, gee es VOR ss ot et pee ee ee 
Tolles’ į 
SOS a os ee a ee o ee ee With “ 
Tolles. immariisn 1-10, on another occasion I saw the. - .- +--+: * 15th 
