THE MICROSCOPE.
Whether for amusement or instruction, there is no instrument so deservedly popular as the Microscope. Other amusements are soon exhausted, but the little world which the microscope reveals is inexhaustible: there is always something wonderful or something new to be seen, and the instruction it affords is unparalleled. Many beautiful objects may be observed by a single lens, which can be folded and carried in the waistcoat-pocket; but there is a limit to the use of such instruments, and the only satisfactory microscope is the compound microscope, which a good optician will supply at a cost of from three guineas upwards. It may be said that cheaper instruments can be had, which appear to do their work well. Perhaps so; but as we are about to recommend only what we know to be worthy of recommendation, we should not name a lower priced instrument than such a one as can be procured of Mr. C. Baker, of No. 244 High Holborn, for three guineas. It is not with any invidious spirit that this name is given. Other opticians may supply microscopes as good at the price, but this instrument will serve to illustrate all we have to say about the microscope, and we shall adopt it as the standard of all our observations.
The microscope we have named is packed in a neat polished mahogany box, with lock and key. The size of this box is 10 in. high, and 6 in. deep, by 7 in. wide. At the top is a brass handle by which it may be carried, and when fully replenished its weight is about 7 lbs. So much for the case and the microscope within it. But we must open the case and take out the instrument. On opening the door we observe at the bottom of the case a neat little mahogany drawer divided in two parts: one part is " racked " for holding glass slides and mounted objects, the other portion will contain small articles of apparatus, which we shall describe hereafter.
We draw out the stand of the microscope, which is clamped to a square of mahogany, so as to ensure greater steadiness, an object of importance in a microscope; from the left side of the case we take the brass tube or body, and screw this to the stand, so that it presents nearly the appearance indicated in our woodcut (Fig. 1). A little cylindrical brass box slides into a hole at the top right-hand corner of the case. This we take down, unscrew the top carefully, take out the combination of glasses set in a neat kind of brass nozzle, which piece of apparatus is usually called the objective or objectglass. There is a screw at one end of this objective and a lens at the other. Let us screw this nozzle or objective into its proper place at the end of the tube or body of the microscope, and then, behold! it is the complete original of which our woodcut is a copy. Having put it together, the next step must be a careful examination of all its parts, and an appreciation of how these parts are to be employed in the examination of objects.
It is not our purpose to enter into a dissertation on the science of optics, for which we have neither room nor inclination; what we most desire is to instruct our reader how to use the mysterious little piece of machinery which has just been unpacked. The "why and wherefore " will be sought by-and-bye, and there are plenty of means of acquiring the theory when it is wanted. Big boys would be more likely to try and use such an instrument at once than to sit down and ponder over " the reason why," and little boys are not a whit less curious or impatient than their elders borne one will perhaps read these pages before he has obtained his microscope, and would like to know how high it stands, so that he may imagine what its appearance would be under a glass shade. For the especial benefit of such a one we have measured the instrument, and declare its full elevation to be 13 inches.
Place the left hand firmly upon the mahogany slab which supports the instrument, then with the right hand hold the top of the tube or body; draw the tube backwards, and it will be found to move easily to any angle, so that a tall boy or a short one, a man standing or a man sitting, can either of them look comfortably down the tube without any danger of dislocating his neck, which might be the case if the tube were fixed bolt upright
As the body moves freely on the pivots the lower portion will be seen to carry with it a circular mirror, which is attached near the bottom; this mirror, by an admirable arrangement of joints, can be turned in any direction. The use of such facility of motion will be seen by-and-bye. Above the mirror is a square brass plate with a round hole in the centre; this is called the stage, and upon it the objects to be viewed by the microscope must be placed. A movable bar passes up and down on the upper surface of this plate, which is useful to retain the slide containing the object in position. Above this stage is the tube with the object-glass screwed in at the lower end, and the eye-piece at the upper end. At the side of the tube or body, near the bottom, is a screw with a milled head, which may be moved by the thumb and finger: this is called the fine adjustment. It will be time enough by-and-bye to speak of its uses. Below the tube are two other milled heads, one on each side. Turn one of them towards you with the thumb and finger: they move easily, freely, and smoothly, and with their motion, behold! the tube of the microscope, with the eye-piece at the top and its object-glass at the bottom, glides up and down just as the operator wishes! A firm, steady, gradual motion here is a necessity in all good instruments. These milled heads and the screws which they move we call the coarse adjustment. Now, having learnt the names of all the parts of the microscope which at present we desire to know, let us put it to work.
No comments:
Post a Comment