The Romance of the Microscope / An interesting description of its uses in all branches of science, industry, agriculture, and in the detection of crime, with a short account of its origin, history, and development :: CHAPTER XVII THE MICRO-TELESCOPE AND SUPER MICROSCOPE

CHAPTER XVII THE MICRO-TELESCOPE AND SUPER MICROSCOPE

Those of our readers who have borne with us thus far may quite excusably have thought that the last word had been attained in the construction of the microscope. It is true that different makers have made various improvements to their instruments, from time to time in recent years, most of them of minor importance but useful in the aggregate. But a few years ago, however, the advent of the Micro-Telescope and Super-Microscope marked an epoch in the manufacture of the microscope. We have shown that great strides were made in scientific investigation when the first simple lenses were manufactured, that there was a lull in microscopic research till the appearance of the compound microscope and now, when the latest instruments are in the hands of scientific workers, further possibilities are opened up.

In all microscopes—the best as well as the cheaper instruments—there is one failing which very early forces itself upon the user. They have very little “depth of focus.” Let us explain exactly what the phrase means. Once or twice in our pages, we have recommended that the fine adjustment should be rotated to and fro while certain objects are being examined. When potato starch grains, for instance, are magnified sufficiently highly to show their characteristic markings, the whole of the grain cannot be seen clearly at one time, because at that magnification the “depth of focus” is slight. The higher the magnification the less is the “depth of focus”; when this quality is absent altogether only one plane of an object can be viewed clearly without re-adjusting the focus. With low magnifications, we may, to a limited extent, have more than one plane of an object in focus.

The same question of “depth of focus” occurs in photography and perhaps an example showing how it affects the camera user may make the matter clearer. Suppose we wish to photograph a landscape having, let us say, a tree in the foreground, a cottage in the mid-distance and a hill in the distance. If our lens is one of large aperture, that is to say admits a considerable amount of light and is also what is known as a long focus lens we shall find, when we view the scene on the ground glass, that when the tree is sharply focussed, the cottage and hill are not clear. When we rack in the camera to get the cottage sharply focussed, the tree and hill will be un-sharp. Similarly when we focus on the hill the tree and cottage remain out of focus. The reason is that the lens in our case possesses little “depth of focus.” The experienced landscape photographer, did he wish all three objects to appear equally sharp could easily attain his object. He would perform the simple operation known as stopping down his lens, that is to say he would gradually close its diaphragm, while viewing the scene on the ground glass. At a certain point everything would be sharp, from foreground to distance. At the smaller aperture of the lens, caused by closing the diaphragm, the depth of focus would be considerably increased, at the same time much less light would be admitted to the camera. Looking upon our object, under the microscope, as comparable to a landscape, seen on the ground glass focussing screen of a camera, it is obvious that, unless our object has no thickness, and this is impossible, we cannot highly magnify its upper and lower surfaces at one and the same time. There are no adjustable diaphragms in the objective so our only course is to examine the two surfaces in turn or to resort to a lower magnification.

By the courtesy of Messrs. F. Davidson & Co.

The Micro-Telescope

1. View taken with ordinary camera. The arrow shows the building illustrated in the plate below; it is 3/4 mile away.

2. The building indicated by the arrow in the plate above, taken from the same standpoint through the micro-telescope.

Apart from any other consideration, the super microscope marks a big advance from the fact that it possesses great “depth of focus.” It is possible, for example, with this remarkable instrument to examine a moss as it grows, with a high magnification and see not a portion of a leaf or a fragment of the stalk, as with the ordinary microscope, but the whole upstanding plant, in stereoscopic relief. It shows us objects exactly as we should see them were we endowed with super eyes, enormously enlarged, in relief and erect. Objects viewed through this instrument are not inverted, as with the ordinary microscope.

A is the microscope proper and is, in all respects, similar to the instrument with which we are familiar, except that its mirror and condenser have been removed. In the fitting provided for the condenser a second microscope is arranged.

This consists of a tube D, an objective F, an ocular C and an inner sliding tube E, the whole fits into the metal case B, G is a stage on which the object is placed and below G, if necessary, a condenser may be fitted.

The instrument owes its remarkable magnifying powers to the fact that the additional microscope B, forms a magnified image of the object on the stage G, at the opening in the stage of the microscope A. This magnified image is still further enlarged by the original microscope. In other words, the power of one microscope is employed on that of another.

The apparatus as we have described it gives enormous magnifications and it is possible, by using a suitable combination of objectives, to obtain a magnification of ten thousand diameters. Expressed in non-technical language, a circle whose actual diameter is equal to the thickness of the paper upon which these words are printed, could be so magnified by the super-microscope that it would appear to be as thick as ten thousand similar pieces of paper but, with this enormous magnification, it is obvious that, even with such a marvellous instrument, the whole of the circle from edge to edge could not be seen at one time. With an ordinary microscope a magnification of one thousand three hundred diameters is considered highly satisfactory. So that there is a great probability of being able to see some of the minute objects which are known to exist, but which have, up to the present, eluded those who would view them, on account of their minuteness. There is a possibility also of discovering a new underworld of which no man has yet dreamed. The man who uses his microscope solely because of the pleasure he derives from it, rather than he who uses it because it is essential to his business or profession, will be more attracted by the micro-telescope. By this we do not infer that the instrument is not useful, as a fact it is of the greatest importance in certain cases, especially for Nature-study work, for the observation of minerals and to the chemist.

Like its sister instrument, the micro-telescope consists of an ordinary microscope to which is attached a specially designed object glass in a tube, which take the place of the condenser. The makers, indeed, provide two of these object glasses—one for viewing objects from one to two feet away, the other for viewing objects from a distance of three feet to the planets, if need be. Once when the instrument was being tested some crumbs were placed on the floor at a distance of four yards and strongly illuminated, and the microscope with a 1-inch objective focussed on the crumbs. With this objective in an ordinary microscope the magnification would be about thirty diameters. Presently some mice came out, and made themselves at home with the crumbs. The mice could be examined at this distance, without their being aware of it, so well that individual hairs were easily visible and about half a mouse was in the field of view. In point of size each mouse appeared about the same as a beaver within a foot or two.

Messrs F. Davidson & Co., 29 Great Portland Street, London, are well known for the high state of perfection to which they have brought the micro-telescope and other instruments connected with microscopy.

The novelty of the micro-telescope will appeal strongly to the Nature lover. At a distance of a few feet a spider can be magnified to the size of a large cat, and it can be watched spinning its web with spinnerettes the size of teacups. Ants at a distance of six feet are seen to be fearsome individuals, six inches in length, and their tiny burdens are so magnified that they appear like yule logs or goodly-proportioned boulders, according to their nature. At a distance of ten feet a wasp may be seen scraping tiny shavings of wood from oak palings by means of its jaws—shavings which it converts into paper for building its nest. Very small insects may be observed as they come into the world from their chrysalis stage. The never-tiring jaws of the caterpillar may be seen at work devouring some favourite leaf—the whole action of biting and swallowing the vegetable matter can be plainly seen. Such interesting events as the tending of green flies by ants, the leaf-cutting habits of the leaf-cutter bee, and a hundred and one other events are all revealed by the micro-telescope and at such a distance that the living objects are not disturbed in their activities, being quite unaware that they are under observation. To the botanist the instrument is no less useful.

In various manufactures, such as ore smelting, and in the manufacture of glass, china and pottery, in enamelling and in certain engineering shops, where it is necessary to examine material at a high temperature, the micro-telescope is a great boon, and, at least, is the means of avoiding considerable physical discomfort. It is used also by architects and surveyors for examining the condition of the factory chimneys, bridges, derricks and the like. To the engineer the instrument is invaluable; we have explained elsewhere how necessary it is that various metals and mixtures of metals should be examined for fractures. Under the high magnification with the ordinary microscope, even with an instrument specially designed for the work, only a very small area can be studied at once. With the micro-telescope a relatively large area may be examined under a high magnifying power.

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. This image is inverted once more in the microscope and so it appears to us erect.

All objects appear in relief and in their proper planes; this is seen in a striking manner by viewing an ordinary photograph through the apparatus, when the various parts stand out as in nature. There is also enormous depth of focus. With the attachment for viewing objects at a short distance, the whole of a tubular shaped flower such as a daffodil may be in focus at once, from the tip of the petals to the bottom of the tube. With the attachment designed for long distance work, objects from twenty yards to sixty miles may be clearly viewed at one and the same time.

A few of the unsolved problems confronting the microscopist are reviewed in our concluding chapter. Whether they will ever be solved we dare not venture to say; but, if they are to be, surely to this latest arrival in the microscopic world and to its companion, the super-microscope, the honours will go.

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