Employment for the Microscope

Baker, H.
London: R. Dodsley

Dutch translation Nuttig Gebruik van het Mikroscoop publishedin 1756 by F. Houttuynas in Amsterdam

On page 434, he describes Leeuwenhoek's single-lens microscopes:

Of Mr. Leeuwenhoek's Microscopes.

Though Mr. Leeuwenhoek's Microscopes are much talked of, very few People are acquainted with their structure and Apparatus, no Figure of them that I remember having ever been made publick: 'tis therefore hoped the Curious will be pleased to see a Drawing of them, taken with great Exactness from those in the Repository of the Royal Society, which are all alike in Form, and differ very little in size from this Drawing, or from one another.

The two sides of one of these Microscopes are shewn Plate XVII. fig. VII and VIII. The Eye must be applyed to the side fig. VII.

The flat Part A is composed of two thin silver Plates fastened together by little Rivets b b b b b b. Between these Plates a very small double-convex Glass is let into a socket, and a Hole is drilled in each Plate for the Eye to look through at c.

A Limb of silver d is fastened to the Plates on this side by a screw e which goes through them both. Another Part of this Limb, joined to it at right Angles, passes under the Plates, and comes out on the other side ; (see fg. VIII) at f: through this runs, directly upwards, a long fine-threaded screw g, which turns in and raises or lowers the stage h, whereon a coarse rugged Pin i for the Object to be fastened to, is turned about by a little Handle k; and this stage with the Pin upon it is removed farther from the magnifying Lens, or admitted nearer to it, by a little screw l, that passing through the stage horizontally, and bearing against the Back of the instrument, thrusts it farther off when there is occasion. The End of the long screw g comes out thro’ the stage at m, where it turns round, but acts not there as a screw, having no Threads that reach so high.

These Microscopes are plain and simple in their Contrivance. All the Parts are silver, fashioned by Mr. Leeuwenhoek's own Hand, and the Glasses, which are excel ent, were all ground and set by himself. He glewed one or at most two Objects on the point of the Pin belonging to each Microscope, and carefully preserved them there; so that each Instrument, being devoted to one or two Objects only, could be applyed to nothing else.

This Method induced him to make a Microscope with a Glass adapted to almost every Object, 'till he had got some hundreds of them: as he says himself, in the 2d Vol. of his Works, pag. 290, Mihi quidem sunt centum centumque Microscopia, &c. All this Trouble and Expence is now saved, by a set of Glasses to be shifted with great Ease, as the subject to be examined may require.

The magnifying Powers of these Glasses come short of some now made, but are fully sufficient for most Purposes. Of the 26 Microscopes I examined, one magnifies the Diameter of an Object 160, one 133, one 114, three 100, three 89, eight 80, two 72, three 66, two 57, one 53, and one 40 times.

On p. 412, Baker gives some advice to researchers who would follow in Leeuwenhoek's steps:

It would not be strictly honest to pass over this Subject, without declaring in Justice to the Memory of Mr. Leeuwenhoek, that not withstanding I have sometimes thought him. mistaken in his Descriptions of Things examined by the Microscope, it has seldom happened, but that afterwards I have found such Descriptions true, and that the Objects I had formerly judged from were not exactly of the same Sort, or in the same Perfection as his: And this I hope will make others cautious, not immediately to determine in Matters of this Nature from a single and perhaps a slight Examination; which I believe too often has been the Case.