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microscopic manipulation; and as it is intended to assist the beginner as well as the advanced student, the very rudiments of the art have not been omitted.
As there is a diversity of opinion as to the best mode of proceeding in certain cases, numerous quotations have been made. Wherever this has been done, the Author believes that he has acknowledged the source from which he has taken the information; and he here tenders his sincere thanks to those friends who so freely allowed him to make use of their works. Should, however, , anyone find his
pages unacknowledged, the author can only plead oversight, and his regret that such should have been
BEFORE entering into the subject of the setting of Objects for the Microscope, the student must be convinced of the necessity of cleanliness in everything relating to the use of that instrument. In no branch is this more apparent than in the preparation of objects; because a slide which would be considered perfectly clean when viewed in the ordinary way is seen to be far otherwise when magnified some hundreds of diameters; and those constant enemies, the floating particles of dust, are everywhere present, and it is only by unpleasant experience that we fully learn what cleanliness is.
Any object which is to be viewed under the microscope must, of course, be supported in some way—this is now usually done by placing it upon a glass slide, which on account of the transparency has a great advantage over other substances. These “slides are almost always made of one size, viz., three inches long by one broad, generally having the edges ground so as to remove all danger of scratching or cutting any object with which they may come in contact. The glass must be very good, else the surface will always
present the appearance of uncleanliness and dust. This dusty look is very common amongst the cheaper kinds of slides, because they are usually “sheet” glass; but is seldom found in those of the quality known amongst dealers by the name of “patent plate.” This latter is more expensive at first, but in the end there is little difference in the cost, as so many of the cheaper slides cannot be used for delicate work if the mounted object is to be seen in perfection. These slides vary considerably in thickness; care should, therefore, be taken to sort them, so that the more delicate objects with which the higher powers are to be used may be mounted upon the thinnest, as the light employed in the illumination is then less interfered with. To aid the microscopist in this work, a metal circle may be procured, having a number of different sized openings on the outer edge, by which the glass slides can be measured. These openings are numbered, and the slides may be separated according to these numbers; so that when mounting any object there will be no need of a long search for that glass which is best suited to it.
When fresh from the dealer's hands, these slides are generally covered with dust, &c., which may be removed by well washing in clean rain-water ; but if the impurity is obstinate, a little washing soda may be added, care being taken, however, that every trace of this is removed by subsequent waters, otherwise the crystals will afterwards form upon the surface. A clean linen cloth should be used to dry the slides, after which they may be laid by for use. Immediately, however, before being used for the reception of objects by any of the following processes, all dust must be removed by rubbing the surface with clean wash-leather or a piece of cambric, and, if needful, breathing upon it, and then using the leather or cambric until perfectly dry. Any small particles left upon the surface may generally be removed by blowing gently upon it, taking care to allow no damp to remain.
We have before said, that any object to be viewed in the
microscope must have its support; but if this object is to be preserved, care must be taken that it is defended from the dust and other impurities. For this purpose it is necessary to use some transparent cover, the most usual at one time being a plate of mica, on account of its thinness; this substance is now, however, never used, thin glass being substituted, which answers admirably. Sometimes it is required to “ take up as little space as possible, owing to the shortness of focus of the object-glasses. It can be procured of any thickness, from one-fiftieth to one-two-hundredand-fiftieth of an inch. On account of its want of strength it is difficult to cut, as it is very liable to "fly" from the point of the diamond. To overcome this tendency as much as possible, it must be laid upon a thicker piece, previously made wet with water, which causes the thin glass to adhere more firmly, and consequently to bear the pressure required in cutting the covers. The process of cutting being so difficult, especially with the thinner kinds, little or nothing is gained by cutting those which can be got from the dealers, as the loss and breakage is necessarily greater in the hands of an amateur. It is convenient, however, to have on hand a few larger pieces, from which unusual sizes may be cut when required.
If the pieces required are rectangular, no other apparatus will be required save a diamond and a flat rule; but if circles are wanted, a machine for that purpose should be used (of which no description is necessary here). There are, however, other contrivances which answer tolerably well. One method is, to cut out from a thick piece of cardboard a circle rather larger than the size wanted. Dr. Carpenter recommends metal rings with a piece of wire soldered on either side; and this, perhaps, is the best, as cardboard is apt to become rough at the edge when much used. A friend of mine uses thin brass plates with circles of various sizes " turned ” through them, and a small raised handle placed at one end. The diamond must be passed round the inner edge, and so managed as to meet
again in the same line, in order that the circle may be true, after which they may be readily disengaged. The sizes usually kept in stock by the dealers are one-half, fiveeighths, and three-quarters inch diameter ; but other sizes may be had to order.
For the information of the beginner it may be mentioned here that the price of the circles is a little more than of the squares; but this is modified in some degree by the circle being rather lighter. If appearance, however, is cared for at all, the circles look much neater upon the slides when not covered with the ornamental papers ; but if these last are used (as will shortly be described) the squares are equally serviceable.
As before mentioned, the thin glass is made of various thicknesses, and the beginner will wish to know which to
For objects requiring no higher power than the oneinch object-glass, the thicker kinds serve well enough; for the half-inch the medium thickness will be required; while, for higher powers, the thinnest covers must be used. The “ test-objects” for the highest powers require to be brought so near to the object-glass that they admit of the very thinnest covering only, and are usually mounted betwixt glasses which a beginner would not be able to use without frequent breakage ; but if these objects were mounted with the common covers, they would be really worthless with the powers which they require to show them satisfactorily.
It may be desirable to know how such small differences as those betwixt the various thin glass covers can be measured. For this purpose there are two or three sorts of apparatus, all, however, depending upon the same principle. The description of one, therefore, will be sufficient.
Upon a small stand is a short metal lever (as it may be termed) which returns by a spring to one certain position, where it is in contact with a fixed piece of metal. At the other end this lever is connected with a finger,” which moves round a dial like that of a watch, whereupon are figures at fixed distances. When the lever is separated from the metal