In 1771, my father published a fourth edition of his Micrographia, in which he described the principal inventions then in use; particularly a contrivance of his own, for applying the solar microscope to the camera obscura, and illuminating it at night by a lamp, by which means a picture of microscopic objects might be exhibited in winter evenings.
It appears[20] from the testimony of M. Æpinus, that Dr. Lieberkühn had considerably improved the solar microscope, by adapting it to view opake objects. This contrivance was by some means lost. The knowledge, however, that such an effect had been produced, led Æpinus to attend to the subject himself, in which he in some measure succeeded, and would, no doubt, have brought it to perfection, if he had increased the size of his illuminating mirror. Some further improvements were made on this instrument by M. Ziehr; but the most perfect instrument of the kind, is that of Mr. B. Martin, who published an account of it in the year 1774.[21] The common solar microscope does not shew the surface of any object, whereas the opake solar microscope not only magnifies the object, but exhibits on a screen an expanded picture of its surface, with all its colours, in a most beautiful manner.
[20] Priestley’s Hist. of Optics, p. 743.
[21] Martin’s Description and Use of an Opake Solar Microscope. The merits and ingenuity in constructing and improving microscopes by this learned optician, seem to be unnoticed by our late author. The following pamphlets by Mr. B. Martin are, among others of his valuable publications, instances of his indefatigable industry. Description and Use of a Pocket Reflecting Microscope, with a Micrometer; 1739. Micrographia Nova, or a New Treatise on the Microscope; 1742. Description of a New Universal Microscope; a Postscript to his New Elements of Optics; 1759. Description of several Sorts of Microscopes, and the Use of the Reflecting Telescope, as an universal Perspective for viewing every Sort of Objects. Optical Essays; 1770. A Description and Use of a Proportional Camera Obscura, with a Solar Microscope adapted thereto, annexed to his Description of the Opake Solar Microscope above-mentioned. Description of a New Universal Microscope; 1776. Description and Use of a Graphical Perspective and Microscope; 1771. Microscopium Polydynamicum, or a New Construction of a Microscope; 1771. An Essay on the genuine Construction of a standard Microscope and Telescope; 1776. Microscopium Pantometricum, or a new Construction of a Micrometer adapted to the Microscope. The most essential articles in the above works will be hereafter described. Edit.
About the year 1774, I invented the improved lucernal microscope; this instrument does not in the least fatigue the eye: it shews all opake objects in a most beautiful manner; and transparent objects may be examined by it in various ways, so that no part of an object is left unexplored; and the outlines of all may be taken with ease, even by those who are most unskilled in drawing.
M. L. F. Dellebarre published an account of his microscope in the year 1777. It does not appear from this, that it was superior in any respect to those that were made in England, but was inferior in others; for those published by my father in 1771 possessed all the advantages of Dellebarre’s in a higher degree, except that of changing the eye glasses.
In 1784, M. Æpinus published a description of what he termed new-invented microscopes, in a letter to the Academy of Sciences at Petersburgh;[22] they are nothing more than an application of the achromatic perspective to microscopic purposes. Now it has been long known to every one who is the least versed in optics, that any telescope is easily converted into a microscope, by removing the object glass to a greater distance from the eye glasses; and that the distance of the image varies with the distance of the object from the focus, and is magnified more as its distance from the object is greater: the same telescope may, therefore be successively turned into a microscope, with different magnifying powers. Mr. Martin had also shewn, in his description and use of a polydynamic microscope, how easily the small achromatic perspective may be applied to this purpose. Botanists might find some advantage in attending to this instrument; it would assist them in discovering small plants at a distance, and thus often save them from the thorns of the hedge, and the dirt of a ditch.
[22] Description des Nouveaux Microscopes inventes par M. Æpinus.
Fig. 1. [Plate III], represents the improved lucernal microscope.
Fig. 1. [Plate IV.] The improved compound and single microscope.