Mathematical Instruments
Suppl. Ch. IX.

# Of Microscopes

These most pleasing and useful Instruments for enlarging and viewing very small Objects, and their Parts, not perceivable by the naked Eye (by reason of their Smallness, and Deficiency in reflecting Light from them to the Eye) and thereby discovering many surprizing Kinds of minute Animals, wonderful in Shape and Motion, as well as some of the Texture, Contrivance, and Structure of natural Bodies, and their Parts, are of two Sorts, viz. single, which consist of one very small Lens, or Globe of Glass or Water, put near to the Eye, or compound ones, consisting of two or three Lenses.

Mr Huygens, in his little Tract upon Microscopes, in his Dioptricks, beginning at page 221, shews, how to make the small Glass Globes for single Microscopes, by melting powdered Glass in the Flame of a Lamp, which will run into various small Globes, and making Choice of such as he found best, which he put into small round Holes, made in a very thin Copper Plate, punched with a Needle, and those he liked best he fixed therein; thus easily making several Microscopes. The well figuring, and polishing such very small Globes, being much more owing to Chance than Design.

Mr Stephen Gray used Drops of Water, placed near the Eye, for single Microscopes. See the Philosophical Transactions, Numb. 221, 223.

Mr Leewenhoeck of Delft in Holland, was doubtless the greatest Judge of the best Kind of Microscopes, as well as the greatest Master in the Use of the Instrument, and has obliged the World with the greatest Discoveries by it of any Man that I know, yet he prefers single Microscopes to compound ones, as may be seen in the Account of Martin Folkes, Esq; given of Mr Leewenhoeck’s Glasses, which by his Will he left to the Royal Society. See Numb. 380. Also a further Account of Mr Leewenhoeck’s Microscopes, by the ingenious Mr Henry Barker, is to be seen at Numb. 458. of the Philosophical Transactions for the Year 1740. This great Man preferred Distinction to great Degrees of magnifying, in which he most certainly was right; for what signifies augmenting the Bulk or an Object, if it and it’s Parts cannot be distinctly and clearly seen; consequently, those are the bed Microscopes, whether single or double, that do this the best. And within these 100 Years there have been a vast Variety of these Instruments made (some single, some double) by ingenious Workmen in England, Italy, Holland, &c. To many, and much dispersed, that few Persons can really tell which are best. Many of them may be good enough, as to the Perfection of the Glasses, but they differ in the lesser essential Contrivances, viz. to move them to the Object, to cast Light upon, and to hold the Object, with the greatest Ease and best Convenience.

The Lenses of single Microscopes are from $$\frac{1}{20}$$ of an Inch, to in Diameter; the manner of making them by one Mr Butterfield, of the Bigness of great Pins Heads, or less, is to be seen in the Philosophical Transactions, Numb. 141. Dr Hook used to take a clear Piece of Glass, and draw it out into long Threads in a Lamp, then he held these Threads in the Flame ’till they run into round Globules hanging to the End of the Threads; and having fixed the Globules with Wax to the End of a Stick, so that the Threads stood upwards, he ground the Ends of the Threads upon a Whetstone, and polished them upon a smooth metal Plate, with a little Putty. Mr Gray makes them somewhat otherwise, See the Philosophical Transactions, Numb. 221, 223, who says, That small round Globules magnified and shewed Objects clearer than Hemispheres. Dr Hook says, he made use of a double Microscope in most of his Observations. See the Preface to his Micrography: and to enlighten his Objects as much as possible, he made choice of a Room with but one Window towards the South, where at the Distance of 3 or 4 Feet from the Window he placed his double Microscope upon a Table, and by a Glass Globe full of Water, and a thick plano-convex Lens he threw the Light upon the Object; or when the Sun shone, he placed a Piece of oiled Paper very near the Object, and with a very large Burning-Glass he threw the Sun’s Rays upon the Paper, so as that a great Quantity of them might be transmitted through it to the Object; but the Paper being subject to take Fire, if the Focus of the Rays fell upon it, instead thereof he put a Piece of plane Glass, not polished, but only rough ground with fine Sand, which when warmed gradually would endure much more Heat than the oiled Paper; and so would suffer more Light to pass through it to the Object; and by this means says he, the Sun’s Light was more equally diffused upon the Parts of the Object than the Sun’s direct Light. In the Night-Time he illuminated his Object with the Light of a Lamp, first refracted through his Globe full of Water, or clear Erine, which refracts more than Water, and then collected into a smaller Spot upon the Object by a plano-convex Lens. He also placed a polished concave Metal on the Side of the Lamp opposite to the Globe, to reflect part of the Rays upon the Globe; and thus he says he could illuminate an Object with a small Lamp as much as it would well bear, and he drew most of the Representations of Objects by the Light of his Lamp.

Note, A double Microscope contrived for viewing Objects by Sun-shine is called by some of the Moderns, a solar Microscope; and without dispute, Objects viewed in Sun-shine will be best perceived and distinguished, provided the Sun-shine be not too great, or the Eye dazzled by the Glare.

I have already hinted, that the World is now full of Microscopes, some better, some worse. Mr Wilson’s Pocket Microscope described in the Philosophical Transactions, Numb. 281. Mr Campani’s and Divini’s. Mr Leuwenhoeck’s. Dr Hook’s. Mr Marshal’s double Microscope, discribed in Dr Harris’s, Lexicon. Mr Culpepper’s and Scarlat’s, Mr Musschenbroeck’s, &c. have been reckoned to be very good. And some of the best Writings upon the Use of the Microscope are,

1. Dr Hook’s Micrography, in Folio, printed at London, in the Year 1667.
2. Mr Leuwenhoeck’s various Tracts, viz. his Arcana Naturæ detecla, in Quarto, printed at Delft, in the Year 1695; his Continuatio Arc anorum Naturæ detectorum, in Quarto, in the Year 1697; his Arcana ope & beneficio exquisitissimorum Microscopiorum detecta, in Quarto, in the Year 1696; his Continuatio epistolarum datarum ad longe celeberrimam regiam Societatem Londinenfem, printed at Leyden, in the Year 1696, in Quarto.
3. John Grendel’s Micrographia Curiosa, in Quarto, printed at Noremburgh, in the Year 1687.
4. Franciscus Fontana’s Observationes Celestium Terrestriumque Rerum.
5. Malpighius’s Anatomia Plant arum; his Tractatus de ovo incubato, de Bombyce, de Vicerum Struclura.
6. Bonnani’s Micrographia Curiosa, in Quarto, printed at Rome, in the Year 1691.
7. Mr Baker’s Treatise of the Microscope, printed at London, in the Year 1741.

There are many others who have given microscopical Observations; in the Philosophical Transactions, and other Tracts, too long to mention. Sir Isaac Newton, in the Philosophical Transactions, Numb. 80, hints at a Reflecting Microscope, and Dr Smith in his Opticks, gives the Dimensions for making one; but I have heard the Contrivance will not do well.