MICROLESTES. See PLAGIAULACIDÆ, MICROLITE (Greek, "small"), a native pyrotantalata of calcium, containing fluorine and also nibium and various other bases. The formula has not yet been satisfactorily determined. Microlite crystallizes in octahedral forms belonging to the isometric system, and the crystals are often very small. It was first found at Chesterfield, Mass., where the crystals were so minute as to suggest the name "microlite." Excellent crystals as much as an inch in diameter have since been found in Amelia County, Va., as well as imperfect ones weighing as much as four pounds. The mineral is usually yellow or brown in color, with a resinous lustre, a hardness of 5.5 and a specific gravity of from 5.5 to 6.1.

MICROMETER, an instrument for measuring minute angles and distances. The "double-image micrometer" is of importance in measuring the diameter of a celestial object; it is an eye-piece containing two halves of a lens, each half being movable by a micrometer screw (q.v.) in a direction parallel to the common diameter. When the halves form one lens the heads of the screws indicate zero. In making an observation of the diameter of a heavenly body the half-lenses are so moved that the image formed by one of them of one limb of the body coincides with the image of the opposite limb formed by the other halflens; the readings of the screw-heads determine the apparent diameter of the body.

μ

MICRON, mi'kron (Greek, "very small"), a unit of length equal to the millionth part of a metre, or the 25,400th part of an inch. It is much used among physicists in connection with precise measurements, and has been officially sanctioned by the International Commission of Weights and Measures. The Greek letter is used as its symbol. Thus "47 μ is read "47 microns." The. names "bicron" and "tricron have been proposed, respectively, for the billionth and trillionth part of a metre, but they have not been generally adopted, and probably will not be. Etymologically, at least, they are monstrosities.

MICRONESIA. To the islands shortly north of the equator in the Pacific has been applied the designation "Micronesia" (Greek, mikros, small; nesos, island). The designation aptly describes the physical appearance of the islands of this subdivision of Oceanica, for they are generally small and generally low, and the section contains a larger proportion of islands of the atoll type than any other subdivision of the globe. Listing the several archipelagoes from the east toward the west we find the Marshall group, with its two chains, the Ratak and Ralik; the Caroline group; the Palau, and the Marianas or Ladrones. In the order of their discovery all of these islands, with the exception of the Marshall group, came under the sovereignty of Spain in the 15th century, and with a single exception remained Spanish until the year after the Spanish War, in which they passed to the German Empire, by purchase, for 24,000,000 pesetas; they remained German until their capture by the naval forces of Japan in October 1914. The single exception to the German purchase from Spain is the island of Guam, which was captured by the United States in the Spanish War in 1898, and now re

VOL. 19-3

mains an important base of American naval strategy in the Pacific. This is the southernmost island of the Ladrones, possesses a good harbor and is 47 miles distant from the island of Rota, its nearest neighbor. Despite the infrequency of rain all of these islands may be regarded as fertile and abundantly productive. The staple product of such agriculture as is practised by the inhabitants is the cocoanut, whose dried meat, known commercially as copra, finds extensive use in the production of oil and feed-cake. In climate, conditions are found such as might be expected in low altitudes in immediate proximity to the equator, but the excessive temperature is very pleasantly moderated by the prevalence of ocean breezes. Lying in the region between the two trade winds precipitation is generally below the normal, and the supply of water is markedly deficient, in some islands the only potable water being that which is obtained by filtration through the beach sand into temporary wells which are dug above high water mark. The islands in general lie outside the hurricane belt, yet at rare intervals they have been visited by destructive gales of this type. The ethnological position of the islanders is as yet imperfectly known; physically and in language they differ from the other inhabitants of the Pacific, and in some particulars they seem to suggest a certain degree of derivation from the races of the southeastern corner of Asia, between Tibet and Cambodia. Within a historic period, the native race of Guam, the Chamoro, have been destroyed in a futile insurrection against the introduction of foreign culture.

In 1850 the greater part of Micronesia came under the influence of American missionaries, who in that year established a station on the island of Kusaie, in 1856 extended their work to the Marshall Islands, and later spread their efforts over all of the eastern Caroline Islands; in this latter field they came into conflict with the Spanish government, and were forced to withdraw. Micronesia, since the discovery period, has been but scantily subjected to scientific investigation, except upon the linguistic side. Consult Christian, F. W., 'The Caroline Islands) (London 1899); Furness, The Island of Stone Money) (Philadelphia 1910); Father Salesius, 'Die Karolinen-Insel Jap' (Stuttgart 1904); Bartolis, Las Carolinas (Barcelona 1885); Cabeza Pereira, 'Estudios sobre las Carolinas (Manila 1895).

MICRO-ORGANISM. See BACTERIA. · MICROPHONE. See ELECTRICAL TERMS. MICROPHOTOGRAPHY, the art of photographing minute objects by combining a camera with a microscope in such a way as to obtain a picture of the object as enlarged by the lenses of the latter instrument; also, the art of making a photograph on a minute scale, by means of reducing lenses, of any object, as a page of print, which may afterward be enlarged by rephotographing it through a microscope. Also called Photomicrography. See PHOTOGRAPHY.

MICROPYLE, the minute opening in the integument of an animal egg-cell, or in the ovule of a plant, by which the spermatozoon in the case of an animal, or the pollen of the plant, enters the egg or ovule to make contact

with the germinating vesicle and effect fertilization.

MICROSAURI, an order of Prosauria. See HERPETOLOGY.

MICROSCOPE, an optical instrument by which images of objects are so magnified that details invisible or indistinct to the naked eye are clearly observed. In the ordinary microscope the magnifying power is interposed directly between the eye and the object, in the manner of a magnifying glass; and although the power may consist of several lenses, they combine as one. See LENS.

gives the first magnified image is the one nearest the object, and therefore called objectglass or objective. The optical part which magnifies the image formed by the objective is the one to which the eye is applied and is called the eye-piece or ocular. This latter, in its common

FIG. 1.

Microscopes are of two types - simple and compound, the former being used for low magnifications, rarely exceeding 20 diameters, whereas the latter may give as high as 4,000 diameters magnification. In the simple form the eye views the object directly (Fig. 1), whereas in the compound form an enlarged image is formed by one lens, which image is magnified by another lens or pair of lenses, at the same time reversing it so that what is at the right hand in the object is at the left hand in the image. (Fig. 2.) A short focus positive lens becomes a simple microscope when used for directly viewing an object; its usual form is that of the Pocket Magnifier, and although generally consisting of a combination of two or more lenses with the view of improving its quality, it always remains optically simple. The most simple forms are one or several convex lenses mounted separately and offering a variety of foci, and hence of magnifying power. These lenses have two defects, one, chromatic aberration, which fringes the images with the colors of the spectrum, most noticeably red or yellow, and blue; the other, spherical aberration, which is most noticeable by the lack of distinctness increasing toward the edge of the field. Improved forms are constructed to overcome these defects. most simple of these is the Coddington lens, originally a section of a sphere, but, as generally made, a thick double convex lens with a circular groove which acts as a diaphragm. The achromatic lens when composed of three lenses, two concavo-convex flint glass lenses enclosing and cemented to a double convex crown glass lens, is the best form. These are usually placed in a folding mounting for pocket use. The simple microscope is also made in more complex form for dissecting purposes, a mechanical construction, more or less elaborate, being added, which provides adjustment for the lens in relation to the object, a platform or stage for the latter, and a mirror for reflecting light to illuminate the object. (Fig. 3).

The

In the compound microscope the lens which

to a focus at the diaphragm cd. At this point it is viewed by the eye lens of the eye-piece and magnified to the size ef. Fig. 4 shows the appearance of the working instrument in which the principles exhibited in the diagram, Fig. 2, are applied. The particular instrument shown is fitted with three objectives of different focus set on a pivot, so that any one of them may be brought into the axis of the tube. There is a rack and pinion for adjusting the focus and micrometric attachments for moving the object on the stage. The tube and stage are pivoted on the two pillars to incline at any convenient angle. The magnification of the compound microscope depends upon three conditions: (1) The power of the object-glass, (2) the power of the eye-piece, (3) the amount of

the objective 150 diameters. A convex lens of one inch focus gives a magnification of about 10 diameters at a distance of 10 inches, and this holds true of a combination of lenses of this equivalent focus as in the eye-piece. If therefore a one-inch focus eye-piece is 10 inches distant from a one-inch objective, the magnifying power is 10 X 10-100 diameters; or, if 5 inches distant, is one-half as great, or 50 diameters. The designation of power is according to the focus of a single lens having the same magnifying power as the series or combination of lenses which make up the objective as well as eye-piece. As the image of the objective is magnified by the eye-piece, it is evident that any defect in the objective is magnified to the same extent, and unless eliminated would seriously interfere with obtaining a distinct image. The main problem, therefore, remains to convey through the objective as many image-giving rays, free from defects, as possible. As a matter of fact, objectives, whatever their power, are composed of a series of lenses whose purpose it is to correct errors which would exist if single lenses alone were used, and the greater the power of the objec

01

29211

FIG. 5.-A low power (3) microscope objec tive of two systems,

FIG. 4.-Compound Microscope. separation of these two optical parts. If the focus of the object-glass is reduced, the power is increased, and the same holds true with the eye-piece. The more the objective and eyepiece are separated, the greater will be the power. It will appear from this statement, therefore, that the magnification of the microscope is unlimited, but the mere magnification of an object is less sought after and is of less value in the modern microscope than its definition or power to disclose detail and structure. The length of tube which connects the eyepiece and objective is limited to from six to eight inches, for the sake of convenience in use. A draw-tube permits the length to be extended to 12 or 13 inches for the highest powers. The standard length of the microscope tube must be closely adhered to or else the optical capacity (correction) of the objective will be disturbed. The power of the eyepiece rarely exceeds 15 diameters and that of

FIG. 6. A high power (1-12") microscope objective of four systems.

tive, the larger the number of lenses required. In the low powers there are generally two systems of lenses, each of which is an achromatic doublet; in the medium powers the principal magnification is obtained by a single front or hemispherical lens and two systems of cemented and corrected lenses; in the high powers it is usual to employ two superposed hemispherical lenses, adding thereto two corrected combinations. As may be supposed, the production of these lenses and setting them in mountings involves the most accurate processes. First of all the various kinds of glass must have fixed and previously calculated properties and be of absolute homogeneity and freedom from blemishes. The production of such glass is in itself a laborious and delicate process. The lenses must be accurately ground and polished to absolutely correct spherical surfaces, truly centred and cemented, then set in suitable mountings without strain at absolutely correct distance and the axes of all in alignment. The efficiency of an objective to gather up rays emanating from an object and form a perfect image depends upon its angular aperture in other words, upon the angle at a point in the axis of the microscope subtended by the diameter of the object in its normal horizontal plane; and this really determines

the visibility of detail (correction for chromatic and spherical aberration being presupposed). On account of the loss of light and inability to obtain sufficient angular aperture in the ordinary way in the very high powers, it is necessary to construct them for immersion contact with the object, and they are then termed "immersion objectives." The immersion medium commonly used is a drop of cedar oil, which has the same refractive index as glass. The connection of the objective with the object by the globule of oil prevents the light rays from scattering. The highest power in general use is the 1/12-inch focus, giving a magnification up to 3,000 diameters, the medium powers are % to % inch, and the low powers from 1 to 2/3 inch.

Having reached the practical limits in the reduction of the focal length of microscope objectives the lens makers turned to the problem of increasing the "numerical aperture" that is, an arbitrary numeral representing the product of one-half of the angular aperture of the objective by the refractive index of the medium between the cover glass of the slide and the outer lens of the objective. A high degree of success has been attained, so that dry lenses of 0.9, water immersion lenses of 1.2 and oil immersion lenses of 1.4 are available (against theoretical calculations respectively of 1.0, 1.4 and 1.53).

To properly adjust the optical parts which have a fixed relation to one another by means of a tube (body) and to hold the object in its proper position in relation to them involves certain mechanical appliances which provide stability, convenience of adjustment and illumination: a rack and pinion provides coarse adjustment and a micrometer screw fine adjustment; both are extremely delicate; the stage or platform for placing the object, and mirror beneath the stage for reflecting abundant light and a base for stability. This aggregate of mechanical parts is called the "stand." The collar at the end of the tube to which the object glass is applied is the nose-piece; double and triple nose-pieces are also made to take two and three objectives, which may be rotated and focused on the object in turn. A mechanical stage provides delicate means of adjusting the object in place of the hands. The high powers require more than the usual amount of light for illumination and a condenser gathers it from the mirror and concentrates it upon the object. Micrometers are provided to determine the amount of magnification and measure the actual size of an object. A camera lucida attachment is made to project the magnified image upon a sheet of paper on the table to facilitate its drawing. Beside the microscope with single tube, there is another in which the rays from the objective are bisected and diverted into a second tube, so that the object may be viewed with both eyes. This is the binocular microscope. A special form of microscope known as the "micro-metallograph" is used for the examination of cold metals. The stage is above, with the objective below it and looking upward. The eye-piece is at the end of a horizontal tube, the light rays being carried into it by means of a prism. Another prism on a lower plane is used to illuminate the lower side of

the object. The so-called "thermal microscope" is so modified from the usual model as to have a water-jacket around the objective to keep it cool while examinations are being made of heated objects in the small electric furnace provided as an accessory with the metallurgist's microscope. So far as our knowledge of the action of light and the constitution of visual images goes, the best microscopes now made realize about the limit to which the seeing powers of the instrument can be brought, although experiments with especially controlled illumination, now in progress, may result in advancement in this direction. Nevertheless the field of research and discovery into which the microscope has as yet not penetrated, and which are within its powers, are almost unlimited.

The microscope is used as a necessary accessory in a large number of the sciences and in many industries. It is, primarily, the assistant of the teacher of biology, botany, bacteriology, histology, pathology and the allied branches of science. The medical profession employs it in the examination of the urine, blood and of cancerous and tumorous growths, as well as in searching for the parasites of the body, fungi which infest the hair and skin and for diagnosing febrile diseases. For the examination of steel, iron and other metals to determine their intimate structure, the microscope is extensively used. Its use for the detection of adulterations in foods, drugs, paints, earths, starches and many other substances is often the only effective method of working. The Bureau of Animal Industry of the United States government depends wholly on the microscope for the detection of living parasites in the flesh of animals slaughtered for food. The microscope is used in many industries for counting fine lines, threads and fibres, and for determining the physical structure of cements, emulsions and other substances. The finest possible measurements of space are made with the microscope to which a filar micrometer is applied, and with it the rate of growth in plants is determined.

The use of the microscope for photography also embraces an extremely wide and useful field. Photographs of minute objects enlarged as much as 5,000 diameters (25,000,000 areas) can be produced in this manner, and a permanent record made which can also be used for reproduction by the usual printing processes for the illustration of books, etc. Recently the movements of insects and other small creatures have been reproduced by a biographic microscope, and moving pictures of the unseen world are now presented to audiences as a means of amusement and education.

The microscope was invented between 1590 and 1609 the honors being divided between Hans and Zacharias Janssen, two Hollanders, and that greatest of early opticians, Galileo. From its early form, consisting simply of a double or plano-convex object lens with an eyepiece of a single convex lens to magnify the image, it developed by gradual stages until the latter part of the 18th century, without becoming much more than a toy for the amusement of dilettante. As a matter of fact nearly every form of accessory which is in use at the present time was devised and used in some form,

but the desire for the ornamental and extraordinary rather than the practical was everywhere manifest. With the awakening of general interest in scientific investigation, the microscope began to be used as a tool to accomplish heretofore impossible results. This led to more practical forms of construction, and at last to their production in large quantities and at a cost which placed them within the reach of laboratories and individuals. In 1820 Fraunhofer invented a complete system of computation for telescope lenses, and Seidel and Steinheil soon followed with formulas for photographic lenses. In 1840 the Gauss theory was introduced and workers in optics applied this theory to computing lenses for the microscope. In the early 70's Professor Abbe of the Zeiss optical works at Jena produced computations for microscope lenses which placed them in the front rank of scientific appliances. Among the early American pioneers in the optical improvement of the microscope, the names of Robert Tolles and the two Spencers stand prominent. By their extraordinary manual skill and knowledge of optical principles, they succeeded in producing lenses which, in the case of one by Tolles, had a focal length of 1/75 inch, the highest power objective which has ever been constructed. It was found in practice, however, that, through inability to increase the angle of aperture, these lenses gave no advantage over those of longer focus, and it is now rare to find an objective of less than 1/16 inch focus. With the introduction of the new optical glasses by the Jena works in 188692, new corrections were possible with micro scopic systems, and the phosphoric acid and boric acid glasses were especially useful to the microscope makers. But the greatest advance was made by the discovery of fluorite as a lens material, permitting the flat curvatures necessary in the correction of spherical aberration. The resolving power of microscope lenses was greatly increased and the problems of their manufacture materially simplified by the invention by Tolles of his "duplex front" objective, a construction which was voted impractical by the experts of the time, but which has since superseded all others in the construction of high-power lenses. By the application of Tolles' correction formulas to the Jena glass lenses a new series of very superior microscopic systems was produced in 1911 by Winkel of Göttingen, notable particularly for brightness and sharpness of the image. See MICROSCOPY, CLINICAL; ULTRAMICROSCOPE.

Bibliography. Carpenter, W. B., The Microscope and Its Revelations' (Philadelphia 1901); Gage, S. H., 'The Microscope' (Ithaca, N. Y., 1911); Hovestadt, H., Jena Glass and Its Scientific and Industrial Applications' (London 1902); Spitta, E. J., Microscopy: The Construction, Theory and Use of the Microscope (New York 1907); Zeiss, K., 'Microscopes and Microscopical Accessories (Jena, Germany, 1906).

MICROSCOPE, Solar, a form of microscope in which the illumination is gained from the condensed rays of direct sunlight. It is used for projection purposes where a very powerful light is needed to exhibit the microscopic images upon a screen.

MICROSCOPIUM, in astronomy, one of the 14 constellations which Lacaille added to

the heavens in connection with his work at the Cape of Good Hope. It is a very inconspicuous constellation, its brightest star being of only 5.1 magnitude.

MICROSCOPY, Clinical, the use of the microscope in the diagnosis of disease. The microscope, ever since its first construction, has been used in the study of disease processes, but only within comparatively recent years has it attained its present importance as an adjunct in the clinical diagnosis of many different types of disease. Owing to the development of knowledge of parasitic and infectious diseases, the physician of to-day is better able to make an accurate diagnosis by means of the microscope than were his forefathers. The microscope may be used not only to confirm a diagnosis which has been made by ordinary clinical methods, but it may abbreviate such clinical examination, or by it a diagnosis may be made without such preliminary examination. Thus at the present time consumption of the lungs may be microscopically diagnosed by an examination of the sputum, though the patient be 1,000 miles away, and in the same manner a number of diseases of allied forms may be recognized by certain minute evidences interpretable by the microscope.

The most important of the intestinal parasites that can be thus identified are the tapeworm, roundworm, hook-worm, fluke-worm and pin-worm. In all of these the physician of the present time, by a microscopical examination of the fæces, can detect the presence of the eggs of the different kinds of worms and make a definite diagnosis. It is not necessary for parents to guess at the presence of worms and to treat their children "on suspicion." The presence or absence of worms can be accurately and definitely determined by a competent microscopist. Not only can a diagnosis of worms in general be made, but the precise kind of worm can be known by the characteristic configuration of the eggs. Examination of the fæces by the microscope can further detect various forms of indigestion and various kinds of inflammation in the intestinal tract.

As already indicated, tuberculosis can be told by an examination of the sputum, and the bacillus of tuberculosis can also be identified if it invades other organs of the body, notably the skin, bladder, kidneys, etc. The presence of tuberculosis in milk can also be demonstrated by the microscope. The influenza bacillus, the bacillus of diphtheria, the organism of cholera, of dysentery, of malignant pustule, of blood-poisoning, of pneumonia, of actinomycosis, etc., can all be identified by a microscopical examination, as also can a number of diseases due to animal parasites in the body, other than intestinal worms. Thus there is no excuse for the general diagnosis of malaria unless the exact confirmatory evidence of the malarial parasite is found in the blood. The presence of Trichina in the body can also be learned by the peculiar changes that take place in the blood, and the blood-parasite Filaria (see FILARIASIS), which causes a variety of conditions in the tropics, is recognizable under the microscope. Further, the microscopical examination of the blood itself offers a large field for clinical microscopy; a field which is very rapidly widening and offering increasing evidence of the value of this class of exam