Sir Isaac Newton having discovered his celebrated theory of light and colors, was led to improve the telescope, and apply his principles most successfully to the construction of a compound reflecting microscope. On the 6th February 1672, he communicated to the Royal Society his designs of a microscope by reflection. It consisted of a concave spherical speculum of metal, and eye-glass which magnified the reflected image of any object placed between them in the conjugate focus of the speculum. He also pointed out the proper mode of illuminating objects by artificial light, as he describes it, of any convenient color not too much compounded, mono-chromatic.

We find other two plans of this kind; the first that of Dr. Robert Barker, and the second that of Dr. Smith. In the latter there were two reflecting mirrors, one concave, and the other convex: the image was viewed by a lens. This microscope, though far from being executed in the best manner, performed, says Dr. smith, very well, so that he did not doubt it would have excelled others, hade it been properly finished.

In 1738, Lieberkuhn invention of the solar microscope was communicated to the public. The vast magnifying power obtained by this instrument, the colossal grandeur with which it exhibited the minutiae of nature, the pleasure which arose from being able to display the same object to a number of observer at the same time, by affording a new source of rational amusement, increased the number of microscope observers, who were further stimulated to the same pursuits by Mr. Tembley famous discovery of the polype. The discovery of the wonderful properties of this little animal, together with the works of Mr. Trembley, Mr. Baker, and Mr. Adams, combined to spread the reputation of the instrument.

In 1742, Mr. Henry Baker, F.R.S. published an admirable treatise on the microscope. He also read several papers before the Royal Society on the subject of his microscope discoveries. In the wood-cut at the end of this chapter we have represented an elegant scroll pocket microscope with a speculum, described by him as a new invention.

In 1770, Dr. Hill published a treatise, in which he endeavors by means of the microscope to explain the construction of timber, and to show the number, the nature, and office of its several parts, their various arrangements and proportions in the different kinds; and he points out a way of judging, from the structure of trees, the uses they will best serve in the affairs of life.

M.L.F Delabarre published an account of his microscope in 1777. It does not appear that it was superior in any respect to those that respect to those that were then made in England. It was inferior to some; for those made by Mr. Adams, in higher degree, expect that of changing the eye-glasses.

In 1774, Mr. Adams, the son of the above, improved his father invention, and rendered it useful for viewing opaque as well as transparent objects. This instrument, made and described by him, continued in use uptown the time of the invention of the achromatic improvement, proposed and made in 1815 for Amici, who subsequently gave so much time to the investigation of polarized light, and the adaptation of a polarizing apparatus to the microscope.