As so great an interest is taken, at the present time, in the various N. H. courses, and as several of these courses have a more or less elaborate system of laboratory work with the microscope, it was thought that a brief sketch of the instrument and its possibilities would be acceptable.

The beginning of the microscope of to-day is traceable to the small, single lens instrument of the sixteenth century, called at the time Vita pulicaria, or flea-glass, because by its aid the true beauty of the flea, in outline and detail, was first brought clearly before the public eye. Aside from the great advantage accruing to mankind from a just appreciation of the flea, the learned men of the time declared that, with this wonderful machine, they had discovered many new monsters; and one savant affirmed that he had seen the devil himself.

It is no wonder, in view of these facts, that the microscope received much attention, and as early as the first part of the seventeenth century the "compound microscope" was invented. Henceforth the progress of the instrument was that of mechanical skill and scientific knowledge. The establishing of the theory of Achromatics, late in the last century, brought the microscope rapidly forward, and the date of 1807 finds us with an "a chromatic microscope," embracing all the main features of the present instrument.

There is a popular idea that the utility and magnification of a microscope depend somehow on its size and formidable appearance. How false this conception is can be learned any day by a visit to the work-shop of a practical microscopist. His resplendent "double barrel" binocular is kept carefully under cover, at ordinary times, and only brought out for exhibition, while the real work is done with a smaller and apparently inferior instrument.

The comparative independence of a microscopist from an elaborate stand arises from the fact that the true value of his work is due to his experience and the magnifying power of the lenses which he uses. The objective, or system of lenses nearest the object, and ocular or system nearest the eye, are the two parts upon which this magnifying power depends, the burden of the work always being put upon the objective.

In this country and in England the objectives and oculars are named in inches or fractions of an inch, relatively to the focal length of a simple lens which will produce the same magnification. Thus taking the focal length of the eye as ten inches, a one inch objective magnifies ten diameters, a 1-50 inch objective, five hundred diameters; a 1-100 objective, one thousand diameters; (the highest powers made). When the ocular system is added, the magnification is equal to the product of the magnifying powers of the objective times the ocular. For instance, a two inch vocular and a 1-5 objective magnify two hundred and fifty diameters. As oculars are made up to 1-8 and objectives up to 1-100, it is easy to see that the magnification resulting from these two would be almost fabulous; but these high powers are not practical and the use of a magnification of over five or ten thousand diameters is???are. The highest magnification attained by the leading German optician, Schenk, is 6,5000 diameters.

There was early an idea that the action of many supernatural forces would be discovered by the powerful eye of the microscope; and the microscopist of the last century was regarded, by his servants and others, as somehow in league with that devil, whose discovery was due to the savant and the humble "flea glass" of the century before.