nachet’s microscopes. 
two prisms fixed at b b' in the tubes, which are placed at right 
angles to the lower prism A; by this 
second reflection, the reversed image of 
the first reflection, being again reversed, 
is made to correspond with the natural 
position of the object. 
91. An interesting variety of this form 
of instrument, which may he called a 
binocular microscope, is shown in 
fig. 44. In this case the two tubes, B c 
and b' c', containing the two eye-pieces, 
are placed parallel to each other, the 
distance between them being regulated 
by the screws v v; if this distance be 
so adjusted as to correspond with the 
distance between the eyes of the same 
individual, the microscope may be used 
with both eyes, in the same manner as 
a double opera-glass. This has the 
advantage of giving a stronger ap¬ 
pearance of relief to the objects viewed, 
which is especially desirable for a certain class of objects, such as 
crystals. 
92. A triple microscope, upon the principle above described, is 
shown in fig. 45, p. 81, where A is the object-piece, b the multiple 
prism, and c, c' and c” the three eye-tubes, 
A similar instrument, with four eye-tubes, including figures to 
illustrate the mode of observing with it, is shown in fig. 46, p. 33. 
One of the advantages of this class of instruments is, that a 
professor and one or more of his pupils may view the process of a 
microscopic dissection which with a common microscope would be 
impossible, and to which the solar microscope would be inap¬ 
plicable. Microscopic dissections, in general, can only be exhibited 
to those who do not execute them, by their ultimate results. Any 
phenomena which are developed in their progress, can only be 
made known to others by description ; and it is not necessary to 
say, how imperfect such a mode of communication must be, com¬ 
pared with direct observation. 
87 
