Perfectionné par Charles Chevalier Ingénieur Opticien Breveté, Palais Royal 163 à Paris
Solar microscope, c. 1840
Extracted from the translation of Ganot's Éléments de Physique, 1868 (3rd edition)
Solar microscope. The solar microscope is a magic lantern illuminated by the sun's rays which serves to produce highly magnified images of very small objects. It is worked in a darkroom : fig. 602 represents it fitted in the shutter of a room, and fig. 603 gives the internal details.
The sun's rays fall on a plane mirror, M, placed outside the room, and are reflected towards a condensing lens, l, and thence to a second lens, o (fig. 603), by which they are concentrated at its focus. The object to be magnified is at this point; it is placed between two glass plates, which, by means of a spring, n, are kept in a firm position between two metal plates, m. The object thus strongly illuminated is very near the focus of a system of three condensing lenses, x, which forms upon a screen at a suitable distance and inverted and greatly magnified image, ab. The distance of the lenses o and x from the object is regulated by means of screws, C and D.
As the direction of the sun's light is continually varying, the position of the mirror outside the shutter must also be changed, so that the reflection is always in the direction of the axis of the microscope. The most exact apparatus for this purpose is the heliostat, but as this instrument is very expensive, the object is usually attained by inclining the mirror to a greater or less extent by means of an endless screw B, and at the same time turning the mirror itself round the lens l by a knob A, which moves in a fixed slide.
The solar microscope labours under the objection of concentrating great heat on the object, which soon alters it. This is partially obviated by interposing a layer of a saturated solution of alum, which, being a powerfully athermanous substance, cuts off a considerable portion of the heat.
The magnifying power of the solar microscope may be deduced experimentally by substituting for the object a glass plate marked with lines at a distance of 1/10 or 1/100 of a millimeter. Knowing the distance of these lines on the image, the magnifying power may be calculated. The same method is used with the electric light. According to the magnifying power which it is desired to obtain, the objective x is formed of one, two, or three lenses, which are all achromatic.
The nature of the signature on this microscope, Perfectionné par Charles Chevalier Ingénieur Opticien Breveté, Palais Royal 163 à Paris, suggests that Charles Chevalier perfected this type of instrument. His modification to the solar microscope consisted of the addition of an amplifying lens above the objective. The following quote is extracted from the article by G. Devbon, M.D. from the American Journal of Microscopy and Popular Science, 1878.
"I have as yet only alluded to the amplifier as used on the telescope. I will now give its gradual introduction in the microscope. About the year 1823, Charles Chevalier, an optician of note, in Paris, France, applied the plano-concave lens (achromatic, I believe) to the uppermost end of the achromatic doublets used on the simple microscope, for the two-fold purpose of amplifying the image, and increasing the distance between the objective and object. In the year 1825, Charles Chevalier improved the construction of the solar microscope, and added to it an amplifier, consisting of a plano-concave achromatic lens, placed in back of the achromatic objective. M. Arthur Chevalier, his son, continues to make solar microscopes, with the amplifier, (lentille plano-concave achromatique.)"
Charles Chevalier (1804-1859) was located at the address marked on this instrument between the years1832 and 1849.
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