While the astronomer has been reducing the heavenly bodies to the dimensions of his stereoscopic slide, the anatomist has been lifting the invisible by the aid of his microscope into palpable dimensions, to remain permanently recorded in the handwriting of the sun himself. Eighteen years ago, M. Donne published in Paris a series of plates executed after figures obtained by the process of Daguerre. These, which we have long employed in teaching, give some pretty good views of various organic elements, but do not attempt to reproduce any of the tissues. Professor O.N. Rood, of Troy, has sent us some most interesting photographs, showing the markings of infusoria enormously magnified and perfectly defined. In a stereograph sent us by the same gentleman the epithelium scales from mucous membrane are shown floating or half-submerged in fluid,--a very curious effect, requiring the double image to produce it. Of all the microphotographs we have seen, those made by Dr. John Dean, of Boston, from his own sections of the spinal cord, are the most remarkable for the light they throw on the minute structure of the body. The sections made by Dr. Dean are in themselves very beautiful specimens, and have formed the basis of a communication to the American Academy of Arts and Sciences, in which many new observations have been added to our knowledge of this most complicated structure. But figures drawn from images seen in the field of the microscope have too often been known to borrow a good deal from the imagination of the beholder. Some objects are so complex that they defy the most cunning hand to render them with all their features. When the enlarged image is suffered to delineate itself, as in Dr. Dean's views of the _medulla oblongata_, there is no room to question the exactness of the portraiture, and the distant student is able to form his own opinion as well as the original observer. These later achievements of Dr. Dean have excited much attention here and in Europe, and point to a new epoch of anatomical and physiological delineation. The reversed method of microscopic photography is that which gives portraits and documents in little. The best specimen of this kind we have obtained is another of those miracles which recall the wonders of Arabian fiction. On a slip of glass, three inches long by one broad, is a circle of thinner glass, as large as a ten-cent piece. In the centre of this is a speck, as if a fly had stepped there without scraping his foot before setting it down. On putting this under a microscope magnifying fifty diameters there come into view the Declaration of Independence in full, in a clear, bold type, every name signed in fac-simile; the arms of all the States, easily made out, and well finished; with good portraits of all the Presidents, down to a recent date. Any person familiar with the faces of the Presidents would recognize any one of these portraits in a moment.