Compound microscope

“ We have now manufactured and sold over 71000 compound microscopes and 31000 oil immersion objectives, a large number of which are used in the laboratories of Universities, Colleges, and other Educational Institutions of the United States.
We are prepared at New-York and Chicago to repair our instruments or make alterations at short notice and at lowest prices. The optical part of a microscope should invariably be sent to the maker, as he is best in a position to repair same and has an added interest to bring a lens back to its original quality or even improve it. ”

“ In the compound microscope the initial image, formed by the object-glass, is further magnified by another set of lenses, forming the eye-piece, by which the diverging rays of the virtual image are brought together to a focus at the eye-point; and when viewed directly, the eye sees an imaginary image, as in a simple microscope, whilst, when the rays are allowed to fall upon a screen, they form a real image of the object, larger or smaller, as the screen is farther from or nearer to the eye-point. ”

“ Even after the improvement of the simple microscope by the use of doublets and triplets, the long course of the rays, and the large angular pencil required in the compound instrument, deterred the most sanguine from anticipating the period when they should be conducted through such a path free both from spherical and chromatic errors. Within twenty years of the present period, philosophers of no less eminence than M. Blot and Dr. Wollaston predicted that the compound would never rival the simple microscope, and that the idea of achromatizing its object-glass was hopeless. ”

“ Although it is possible to employ compound microscopes of such a high magnifying power in the investigation of certain classes of objects, all ordinary preparations are best seen under a power of 500 or 600 diameters. It would be utterly impossible to give our readers the slightest idea of the benefits conferred on the human race by this marvellous instrument. Suffice it to say, that no naturalist or surgeon ever attempts the most simple investigation into the structure of any body without the aid of the microscope. ”

“ Let us describe a more refined compound microscope than the one we constructed in our darkened room. The optical parts, that is to say the lenses, are the most important parts of every microscope, upon their qualities depend the degree of efficiency of the instrument; the metal portions, known collectively as the stand, contribute to the easier, smoother working of the microscope. ”

“ The cheapest forms of compound microscopes have all the parts we have mentioned, and focussing is carried out by sliding the tube, with its objective and eyepiece, up and down within its holder, in order to bring the objective further from or nearer to the object. ”

“ With such powers as those with which we shall have to deal, it will rarely happen that, for example, a bottle of water in which no life is visible will be worth the carrying-home; whilst, on the other hand, a few months’ practice will render it not only possible, but easy, not only to recognise the presence, but to identify the genus, and often even the species, of the forms of life present. Moreover, these low powers, affording a general view of the object, allow the relation to each other of the details revealed by the power of the compound microscope to be much more easily grasped. ”

“ For a microscope to be a compound one, its essential qualification is that it should have an object-glass or objective, and an eye-glass or eye-piece, so called because they are respectively near the object and the eye of the observer when the instrument is in use. The microscope consists of a tube or body, and a stand, an arrangement for carrying the body, combined with which is a stage for holding the object, and a mirror for its illumination. To the more modern instrument has been added a substage, to carry a condenser and other accessories. ”

“ Use of the Microscope. To do thorough and satisfactory work in physiology in our higher schools a compound microscope is almost indispensable. Inasmuch as many of our best secondary schools are equipped with one or more microscopes for use in other studies, notably botany, it is much less difficult than it was a few years ago to obtain this important help for the classes in physiology.
Fig. 170.—A Compound Microscope
For elementary class work a moderate-priced, but well-made and strong, instrument should be provided. ”

“ Having obtained a sharp image we remove the paper and gradually advance our second lens towards the first. We soon reach a point where we have a very much larger image of the candle than the first lens gave us; we [53] must fix our second lens at this point for we now have a compound microscope, a very crude one certainly and without the trimmings which make the microscope so useful. Before we proceed to explain what has happened to the light rays we must take our paper screen once more and place it as near as possible to the spot where our eye was situated when we saw the second image. ”

“ Theoretically a simple microscope can be made as powerful as a compound microscope, but in practice the minute size required by the simple lens to give the highest power makes it almost impossible to be used. However, a lens having a reasonable magnifying power can be made in a few minutes for almost nothing. Take a piece of glass tubing, heat one place in a hot flame, hold one end and pull on the other and draw the heated place down to a fine string as shown in Fig. ”

“ The magnifying powers of the compound microscope can be very great, and it is therefore necessary that extreme care should be taken in its manipulation. It will be possible for a clumsy person to do more damage to a good instrument in three minutes than can be repaired in as many weeks. ”

“ Some simple microscopes consist of two or more lenses mounted together in order to increase the magnifying power. The student must distinguish between several lenses mounted together in this way, and the true compound microscope, which is a comparatively complicated optical arrangement, as we shall see presently. When two single lenses are thus mounted together, the power of the combination is equal to the powers of each added together.
There is good reason for supposing that the simple microscope is a comparatively ancient invention. ”

“ It is much better to use a good simple microscope than a poor and cheap compound one; be sure and remember this and not be enticed to buy such an one by any representations as to its great magnifying power. ”

“ Place upon the stage an object, preferably a round diatom or an echinus-spine, and focus it as sharply as possible. Now place the substage condenser in its jacket, and slide it up and down until the image of the object is bisected by the image of the flame.
The centre of the object will now be brilliantly illuminated by rays travelling in the proper direction for yielding the best results. The object is situated at the common focus of the microscope and the condenser, and, whatever means of illumination be adopted, this is the result which should always be aimed at. ”

“ The simplest and, in many ways, the best is to use the bull’s-eye condenser to bring to a focus upon the object the rays of light from some source placed above the stage of the microscope. If light can be obtained from the sun itself, no lens will be needed to concentrate it ”

“ Along with this I purchased every possible accessory,—draw-tubes, micrometers, a camera-lucida, lever-stage, acromatic condensers, white cloud illuminators, prisms, parabolic condensers, polarizing apparatus, forceps, aquatic boxes, fishing-tubes, with a host of other articles, all of which would have been useful in the hands of an experienced microscopist, but, as I afterwards discovered, were not of the slightest present value to me. It takes years of practice to know how to use a complicated microscope. ”

“ It should be deep enough to hold a small fish or newt, and retain it without any undue pressure. When in use it is only necessary to place the animal into it (as shown in Fig. 221) , with some water, and secure it with a glass cover; then immerse the upper tube in a jar of water, while another, at a lower level, maintains a current. When the slide is on the stage of the microscope, one jar should stand on a lower level than the other, the slide being made the highest part of the syphon. The pressure of the atmosphere is sufficient to keep the cover-glass in its place. ”

“ It is a mistake to suppose that direct light is more critical than indirect. As a rule, the student is given to over-illuminate the object. These questions will, however, be discussed further on.
Very many modifications of Gillett’s condenser have, since 1850, become known to microscopists. Ross’s present improved form (Fig. 127) is made to drop into the sub-stage of the microscope, and when adjusted, is an extremely efficient instrument. The optical part is similar to a 4⁄10-inch objective. ”

“ Within the last half-century the use of the microscope, not only as an instrument of scientific research, a tool in the hands of the investigator of the finer organisation of the world of nature, nor even as an adjunct to the apparatus of the chemist or the manufacturer, but as a means of innocent and instructive recreation, has become so firmly rooted amongst us that it seems hardly necessary to advocate its claims to attention on any of these grounds. ”

“ There are three features of this ingenious apparatus which cannot fail to commend themselves equally to the casual worker and the serious microscopist. All objects are seen erect, just as the eye sees them. This is brought about because, as in the case of the super-microscope, we really observe a magnified, inverted image of our object, formed at the spot where the object would be placed were we using an ordinary microscope. ”

“ In many species the markings are so extremely minute that they can only be made out with the highest powers of the microscope and the most careful illumination, so that they serve as test objects whereby the performance of a microscope can be judged by a practical man. ”

“ The method which is the most frequently made use of is the following:—Place the “gathering” containing the Diatomaceæ in a small glass or porcelain vessel, add strong nitric acid, and, by the aid of Bunsen’s burner or spirit-lamp, boil for some minutes. From time to time a drop of the mixture may be put upon a slide, and examined under the microscope to see if all foreign matter be got rid of. When the valves are clean, the vessel containing them must be filled with water, and the whole left for an hour or two, so that all the diatoms may settle perfectly. ”

“ Given an unlimited quantity of a substance for testing purposes it is not always easy to determine its composition. With very small quantities, perhaps less than a tea-spoon full in all, the difficulties of the analyst are increased tenfold and without the assistance of the microscope his efforts would be unavailing, he deals in drops and every drop is precious. Sad to relate this form of testing, known to science as micro-chemical analysis, has been practised to a far greater extent on the continent than in this country. ”

“ It is not the man who possesses the best or most costly apparatus, but the one who best understands the use of that which he possesses, that will make the most successful microscopist. A good observer will discover, with only the aid of a pocket-magnifier, secrets of Nature which have escaped the notice of a whole army of dilettante microscopists, in spite of the advantages which, as regards instruments, the latter may enjoy. ”

“ They cannot be seen in day-time, except the room be darkened, but are seen to the greatest advantage by candle-light. Montucla observes, that [13] when any objects are inclosed within this transparent globule, the hinder part of it acts like a concave mirror, provided they be situated between that surface and the focus; and that by these means they are magnified three times and an half more than they would be in the usual way. An extempore microscope may be formed, by taking up a small drop of water on the point of a pin, and placing it over a fine hole made in a piece of metal ”

“ It may be taken as an axiom with microscopists that “neither the penetrating power nor the high-power defining objective is alone sufficient for every kind of work. The larger the details of ultimate structure, the narrower the aperture—and the converse; the minuter the dimensions of elementary structure, the wider must be the aperture of the objective.” Every worker with the microscope must have satisfied himself of the truth of this statement, when engaged in the study of the movements of living organisms, or defining the intimate structure of the minuter diatoms, or of the podura scale. ”

“ The inorganic kingdom will afford to the microscopist a never-ending number of objects of unsurpassed beauty and interest. The phenomena of crystallisation in its varied combinations can be made 240 a useful and instructive occupation. Although ignorant of the means whereby the great majority of minerals and crystals have been formed in the vast laboratory of Nature, we can, nevertheless, imitate in a small degree Nature’s handiworks by crystallising out a large number of substances, and watch their numerous transformations in the smallest appreciable quantities, when aided by the microscope. ”