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mirror light proceeding from the little object are spread over a large
place, it is necessary to throw as much light as possible upon the
object, else the image will be indistinct. This will be done by
one or more double convex lenses (f-g), which concentrate the
sun's light received and reflected by a plane-mirror (a-b) upon
the object. This instrument was invented by Lieberkühn 1738.
Instead of the sun's light Drummond's Hydrogen-Oxygen flame
(Hydro-Oxygen Microscope) or electric light (Photo-electric
Microscope) may also be used (see § 286).
Remark. The use of this instrument for discoveries in the vege
table and animal kingdom is very well known; it has opened new worlds
and has exhibited in many ways the infinite perfection of God's works
in nature. But the most admirable optical instrument has not been
wrought by men, but comes from God’s hands, this is the eye.
§ 208. 6). The Eye. About the structure of the eye and the
mechanism of vision see 388. The Short-sighted (myopic)
are those who see only at shorter distances, they use double
concave lenses. 391. Long-sight (presbytia) due to the flat
tening of the crystalline lens; in this case double-convex lenses
are necessary. 390.
§ 209 The crystalline lens and the cornea act as two
convex lenses and produce an image on the retina. The cry
stalline lens of a fish is almost spherical, because the refraction
of a ray of light passing from water into the eye is less than that
of a ray passing from the air into the eye! If we want to see
properly in water, we have recourse to a convex lens. Why is
the choroid (the membrane behind the retina) black? Albinos
are wanting this black colour, what is the consequence of this?
When we pass from a dark room into a bright one or in the re
versed case, we see almost nothing in the first moment, why?
In general only young people are short-sighted and only old
people long-sighted, why?
