324 Use of various Microseo^es, [^o^Si.KTff^ 
penetrating power in all microscopes at that time was very low. In 
the old Nobert's test-plate of ten bands, it resolved the sixth well, 
but the seventh is doubtful .At this time Scheck's microscopes were 
considered the best by the most experienced observers, especially 
by Ehrenberg. I am sorry I cannot exhibit a microscope in my 
possession, nearly two hundred years old, and now in good order. 
I have watched with great interest the growing demand for these 
instruments, and the surprising increase in the number manufac- 
tured during the last thirty years. Long ago I made my first 
observations on the scales of Lepidoptera and Coleoptera, with an 
old English microscope, perhaps of Martin, and only partly achro- 
matic. Since then I have used first-class microscopes of Ploesl, then 
those of Scheck (none of them is sufiicient to show the transverse 
lines on the scales of Lepidoptera), later of Oberhauser and Nachet. 
From this time almost every European naturalist gave up using 
microscopes mounted upon high stands, as observations with high 
objectives are more easily and accurately made in a sitting position, 
when the arms can be supported upon the table. The end is not 
attained by placing a microscope with a high stand upon a low table, 
because the hands are less readily guided at a distance from the eyes. 
The English opticians appreciated this, and arranged a strong wooden 
transverse rest for the hands, even in single microscopes. 
I have noticed that foreign students entering the Institute for 
Pathological Anatomy, very soon exchange their high-stand English 
microscopes for short-stand instruments, and even here I was not 
surprised to see the Professor of Pathological Anatomy using a 
short-stand French microscope. 
Doubtless every observer will handle his own instrument to 
greater advantage, but for certain purposes particular constructions 
are preferable ; and indeed I know of no work that would actually 
require a high-stand microscope. I am the better able to judge, 
having examined microscopes of this kind in Germany and England, 
especially those of Fraunhofer, Eoss, Smith, Amici, and others. It 
may be interesting to mention that Nobert's instruments are not 
considered superior. I have examined a first-class microscope with 
an objective fitted for correction, and calculated by him to have a 
power of 500 diameters. The marked yellow light in the Nobert 
microscopes is very trying to the eyes. The mechanical work is 
good, but not remarkable. A kind of screw for fine motion used 
by him is perhaps unknown. A long, strong, steel screw is used ; 
the upper half of the thread of which is turned in the opposite 
direction from that on the under half, and the two halves difi'er 
somewhat in size. By this arrangement the motion of the screw 
moves the instrument only as far as the difierence in the fineness of 
the two halves, and with a strong screw a very fine motion is 
obtained, and "dead point" is impossible. 
