A Compound Achromatic Microscope made by Charles A. Spencer

The microscope is constructed on the model of the smaller microscopes of Charles Chevalier, and like them, can be used either in the horizontal, inclined, or vertical position. It can also be inverted so that the stage is directly over the object.

It differs as to the details of its construction from the instruments of Chevalier, in being supported on a tripod like Prichard's, instead of being screwed into the top of the box, having a safety stage and also a peculiar arrangement by which the object can be moved in azimuth. It has a fine polarizing apparatus and a Lieberkuhn.

There are three objectives of 1/3, 1/7, and 1/12 inch focus and two eyepieces.

With the lower eyepiece, the powers of these combinations are one hundred and twenty five, three hundred and fifty, and six hundred linear diameters respectively. With the high eyepiece, the 1/12 inch objective gives a power of eight hundred, and this with an illumination that makes it a fair, available working power.

A peculiarity of all the objectives, and one on which their excellence, as Mr. Spencer thinks, mainly depends, is the large angle of aperture; this in the 1/7th inch glass is one half greater than in the corresponding power of Chevalier, and in the 1/12th it is nearly double.

Those even moderately familiar with the microscope, will readily appreciate the immense advantage which this wide angle of aperture gives the glasses as a working instrument.

The size of the field is great, the three hundred and fifty power has a field more than double that of the three hundred and twenty-five power of Chevalier.

Of the penetrating and defining power, it is perhaps not necessary that I should speak, when the excellence of the instrument in these respects is vouched for by Prof Bailey, and by the report presented to the New York Lyceum of Natural History by Prof Torrey, Dr. Le Conte, and Mr. Holton.

It is only because I have been in daily habit of using the microscope, and by such use have become familiar with its powers, that I venture to add my own opinion, that the glass is for ordinary use in scientific investigations, as superior to the instruments of Chevalier, Ploessels and Oberhauser, as it has been proved to be when applied to difficult tests. It is both more pleasant and more satisfactory as a working microscope than any I have seen.

It is with no ordinary satisfaction, that I introduce to the scientific men of the United States, a countryman of our own, who has in the very outset of his career, achieved so great a triumph in practical optics as the construction of a compound achromatic microscope which compares most favorably with those made by the first artists in Europe. To him we may look for future displays of scientific skill, which shall make us entirely independent of the old world in this important respect.

The friends of American industry and talent will be pleased to hear that Mr. Spencer has already received orders for microscopes from public institutions and private individuals. Professor Henry has ordered an instrument of high power for the Smithsonian Institute. American patronage, we may hope, will not be wanting to American art.