The opake part may be used in the day-time without a lamp, provided the large lenses at A B be screened from the light.
TO USE THE LUCERNAL MICROSCOPE IN THE EXAMINATION OF TRANSPARENT OBJECTS.
The microscope is to remain as before: the upper part f g r s of the opake stage must be removed, and the stage for transparent objects, represented at Fig. 4, put in its place; the end, Fig. 9 and 10, to be next the lamp.
Place the rough glass in its groove at the end A B, and the objects in the slider-holder at the front of the stage; then transmit as strong a light as you are able on the object, which you will easily do, by raising or lowering the lamp.
The object will be beautifully depicted on the rough glass: it must be regulated to the focus of the magnifier, by turning the pinion a.
The object may be viewed either with or without the guide for the eye; a single observer will see an object to the greatest advantage by using this guide, which is to be adjusted as we have described, page 73. If two or three wish to examine the object at the same time, the guide for the eye must be laid aside.
Take the large lens out of the groove, and receive the image on the rough glass; in this case the guide for the eye is of no use: if the rough glass be taken away, the image of the object may be represented on a paper screen.[29]
[29] A tin cover is sometimes made to go over the glass chimney of the lamp, Fig. 3, with only a small square aperture in front, sufficient to suffer the rays to pass into the microscope: this, by excluding all extraneous rays, adds in many cases most materially to the effect, particularly by day, and when objects are to be represented on the rough glass or screen only. EDIT.
Take out the rough glass, replace the large lenses, and use the guide for the eye; attend to the foregoing directions, and adjust the object to its proper focus. You will then see the object in a blaze of light almost too great for the eye, a circumstance that will be found very useful in the examination of particular objects; the edges of the object in this mode will be somewhat coloured, but as it is only used in this full light for occasional purposes, it has been thought better to leave this small imperfection, than by remedying it, to sacrifice greater advantages; the more so, as this fault is easily corrected, and a new and interesting view of the object is obtained, by turning the instrument out of the direct rays of light, and permitting them to pass through only in an oblique direction, by which the upper surface is in some degree illuminated, and the object is seen partly as opake, partly as transparent. It has been already observed, that the transparent objects might be placed between the slider-holders kl of the stage for opake objects, and then be examined as if opake.