MOUNTING OF MICEOSCOPES. 
76. The attitude of an observer stooping the head to view an 
object in a microscope, whose eye-piece is vertical, is found to be 
attended with much inconvenience, especially if the observation 
be long continued. This has constituted the ground of a very 
general objection to vertical microscopes. Nevertheless there are 
many cases in which it would be inconvenient to place the stage 
in an inclined or vertical position, as, for example, when observa¬ 
tions are made on liquids. In all such cases the model of 
Amici’s stand presents obvious advantages, the observer looking 
horizontally, while the axis of the object-piece is vertical, and 
consequently the stage horizontal. 
Most of the better class of instruments, however, are so 
mounted that any direction whatever can be given to the axis of 
the body. Yarious mechanical expedients are used for accom¬ 
plishing this, most of which are analogous to the methods of 
mounting telescopes. In some, the instrument with its appendages 
is supported upon two uprights of equal height by means of 
trunnions, which pass through its centre of gravity, so that it 
turns upon its supports like a transit instrument, the axis of the 
body being capable of assuming any inclination to the vertical. 
The observer, therefore, may at pleasure look obliquely or verti¬ 
cally downwards, or obliquely upwards, as may suit his purpose. 
Similar motions are also produced by mounting the instrument 
upon a single pillar by means either of a cradle-joint, such as is 
generally used for telescope-stands, or a ball and socket. Stands 
of this form are attended with the advantages of offering greater 
facility for moving the instrument horizontally round its axis. 
In the attainment of all these objects, as well as in the produc¬ 
tion of eye-pieces and object-pieces of capital excellence, the 
leading makers of London, Paris, Berlin, and Vienna, have 
honourably rivalled each other, and it may be most truly said, to 
their credit, that if some have excelled others in particular parts 
of the instrument, there is not one who has not in some way or 
other contributed by invention or contrivance to the perfection 
either of the optical or mechanical parts. 
Much however is also due to the eminent philosophers and 
professors who have more especially devoted their attention to 
those parts of science in which the microscope is a necessary 
means of observation, and foremost among these is the patriarch 
of optical science, Sir David Brewster. It would be difficult to 
name the part of the instrument, or of its accessories or append¬ 
ages, for the improvement of which we are not deeply indebted 
to this eminent man. Among the more recent philosophers who 
have contributed to the advancement of micrography, and by 
whose researches and suggestions the makers have been guided, 
71 
