ABSTRACT There are, perhaps, few instruments of the present day in which theoretical perfection has been so nearly reached in its practical results as in the modern microscope. In saying this, I am of course speaking of it in its most perfect form, in which the highest optical skill is combined with the most consummate mechanical contrivance. A large number of works have been published on the microscope,* on its history and manner of using it, on its manufacture by our chief opticians, and lastly, on the countless variety of objects which nature and art present for its investigation.† Dr. Carpenter’s great work, ‘The Microscope and its Revelations,’ is, in fact, a complete Cyclopædia of itself, in which the above subjects are most ably and fully discussed. The choice, therefore, of a microscope, about which so much has been, and we may safely add is being written, which has become so important an instrument in the hands of the medical student and physiologist, and which opens to the general observer the secrets of minute Nature with a clearness and ease till of late unexampled—the choice at the outset of the most efficient instrument that can be procured by the lover of microscopic research according to his means and requirements is a point of some consequence, and about which I propose now to say a few words. And in doing this, I am merely going to give my own experience in the matter, with such positive and direct advice as may help to guide the inexperienced purchaser in his choice. And firstly, my observations shall be addressed to those who can afford to possess themselves of the most perfect and expensive instruments. I would say, then, to such, what I shall probably have occasion to repeat more than once—Begin by procuring the best microscope stand that the best optician can give you. To explain the optical principles and somewhat complicated mechanism of the compound achromatic microscope with such books as Dr. Carpenter’s, and Mr. Quekett’s, and others before the public, would be altogether superfluous in a little paper like the present. Nor is it necessary to enter into the details of its elementary construction, now that illustrated catalogues within the reach of all are issued by some of our first opticians, with all the various parts figured and described. Besides, it may be taken for granted that a person about to invest a large sum in the purchase of a microscope has a general notion of its form and build. He may fairly be supposed to know the eyepiece from the object-glass, why they are so called, and that on the union of both depends the magnifying power. He may be supposed to know that the stand of the microscope usually consists of two supports, which carry the body into which the glasses fit, together with the stage on which the object rests, and the apparatus necessary for illuminating the object.