OPTICAL PROJECTION
182
dependent approval, especially in first-class public institutions ;
and, so far as I can learn anything at all about them—which
it has been most difficult to do—their success has been in
precise proportion to the degree in which the same general
arrangements have been adopted, though I have not as yet
heard of equal results having been obtained. I therefore con¬
fine myself to what I know and have myself openly tested in
various public demonstrations. Moreover, everything in this
chapter except the description and explanation of the instru¬
ment in detail, will apply equally to others in proportion to
the efficiency of their performance.
92. The Oxy-hydrogen Microscope.—Fig. 102 gives a sec¬
tion of the instrument as constructed for the oxy-hydrogen light.
u represents the lantern condenser, which 1 prefer to make
y inches in diameter and of triple form, so as to take up an
angle of 95°, and bring the rays to a focus, if let alone, at
about G inches in front of the front lens. If the microscope
be required to fit an ordinary 4-inch lantern front, the arrange¬
ment must be slightly different, the lime being in this case
pushed up so as to give an approximately parallel beam with
the ordinary double condenser, while a third lens either slides
or racks in the back-end of the microscope, so as to bring
the parallel rays to a focus corresponding in character to the