A. THE STUDENT MICROSCOPE
B. THE MODEL MICROSCOPE.
This microscope made by the Bausch and Lomb Optical Co., of Rochester, N. Y. , is represented in plate IV, one-third natural size. It is a rather larger instrument, of convenient form and good workmanship, having two pillars instead of one. The coarse adjustment is made by a rack and pinion movement, the large milled heads of the pinion appearing in the plate just behind the compound body; this adjustment being more convenient though not more precise, in skillful hands, than the adjustment by sliding tube. The fine adjustment screw is in the same position as before, though acting upon a clock spring system, to be described hereafter, instead of upon a lever. The stage is round, and concentric to the optical axis of the instrument, as are all other round stages worth mentioning and to it may be added an extra revolving plate with a movable object carrier, by which means fhe adjustment of the object beneath the objective is much facilitated. The diaphragm, seen just beneath the stage, or other substage apparatus, is slipped into a substage ring provided for that purpose.
C. THE ACME MICROSCOPE
Somewhat similar to the last in size and general efficiency is the new model Acme No. 4, represented in Plate V, made and sold by James W. Queen & Co., of Philadelphia. In this instrument the fine adjustment screw is removed to an exceptional location below the limb, and the pinion of the coarse adjustment is placed very high, close to the top of the limb, in order to secure the long range of adjustment required for low power objectives. The diaphragm, being attached to a movable arm, can be swung out of position, as seen in the cut, when not in use, and a substage ring, also shown in the cut, attached in its place for the reception of an illuminating lens or other apparatus. A material advantage of this stand is the possession of a body sufficiently large for oculars of ample size; thus admitting adequate oculars of its own and permitting the frequently convenient interchange ot any oculars, not exceeding that reasonable size. The diameter of the ocular is about 1 1/4 inch (32 mm.), which is the size recently recommended as a standard by the committee on oculars of the American Society of Microscopists, but not yet acted upon by the society. A larger and more elaborate Acme stand, No. 3, by the same manufacturers, has a body of the same size, but possesses a rotating stage and a substage somewhat like those in Plate X the substage being attached, however, to the same bar as the mirror, as in Plate IX.
D. THE NEW STUDENT STAND.
Another excellent instrument of the same grade, of the latest American type is the New Student Stand, made by Walter H Bulloch of Chicago, and represented 2/5 natural size in Plate VI. The peculiarity of this instrument, as compared with the preceding, is the possession of Mr. Bulloch’s form of fine adjustment described hereafter. A sliding object carrier which can be adapted to the stage is shown lying near the foot of the stand.
E. THE PHYSICIANS’ STAND.
A very solid and serviceable instrument of this type is the Physician's Microscope of L. Schrauer of New York, shown in Plate VIII A. The body is large, admitting an ocular of 32 mm. in diameter, and is adjustable by means of its drawtube to any length from 16 to 25 cm or more. The diaphragm is inserted in the stage; and a glass sliding stage is provided, in the Zentmayer style held in position by a spring with ivory tip. Such a stage has a smooth motion and wide range, is available for use with the Maltwood finder (a photographed scale of great use for recording the exact location of mounted objects on a slide and enabling them to be promptly found when wanted again), and is unaffected by those reagents which might in certain cases, mar a brass stage. The joint by which this stand is inclined has a set screw for securing it in any position. The disk of the swinging mirror bar is graduated as in all the higher class stands of this type, for the purpose of determining the obliquity of illumination or the angular aperture of objectives.
F. THE (CONTINENTAL) STUDENT STAND.
While the stands heretofore and hereafter described may be considered as representing the characteristic American type, there have always been some observers who preferred the small compact stands of the French and German model, known as the continental style. Some makers have accordingly adopted a model of this type. Mr. J. Grunow, of New York, one of the earliest American makers, has always been distinguished for this class of stands, and his excellent workmanship has gone far toward making them popular for medical and histological work. His Student Stand No. 2, represented by Plate VII, is a very efficient instrument of this class, a solid little stand, with short body and limb, a drawtube, a low square stage with included rotating diaphragm, and a heavy horseshoe base.
G. THE ILLUSTRATOR’S STAND.
Of somewhat erratic model is the microscope called the Illustrator’s. It is made by T.H. McAllister of New York, and shown in Plate VIII B. It is one of the simplest and most practical of those designed to hold several objects at once. It consists of a broad circular base from the center of which rises a pillar that carries a mirror, a circular stage 25 cm. in diameter rotating concentrically about the pillar, and at the top a horizontal transverse bar with its vertical compound body. The body is focussed by sliding through a tube in the transverse bar, the motion being controlled by a pin working in a spiral slot. The stage is capable of carrying twelve slides, radially, at an equal distance from its center, which can be successively brought under the lenses by rotating the stage. The microscope is best adapted to large objects under low powers. It is adapted to certain uses in teaching, where a number of forms are to be shown in comparison with each other to a class. In research, its use is mainly limited to the rapid comparison of objects, as in the classification of unfamiliar objects, the study of adulterations, or the comparison of samples of merchandise.
H. THE HISTOLOGICAL STAND.
This stand, made by Mr. Zentmayer, and represented, with the addition of the Wenham Binocular arrangement, Fig. 16, in Plate IX, is of the same size as his Student Stand, most of the castings being identical, but is a far more efficient instrument. This superiority is due mainly to the possession of a substage, a horizontal ring or short tube, designed to support the diaphragm or other apparatus that may be required between the stage and the mirror. This substage is carefully centered around the axis of illumination between the mirror, in whatever position it may be placed, and the object on the stage; and it has a smoothly sliding vertical movement by which it may be readily located at any point of that axis. This stand is made with a glass sliding stage, or with a round rotating stage, if desired. In the monocular form, the cost may be reduced by substituting for the rack and pinion coarse adjustment a sliding tube like that in Plate III. It is most commonly made monocular, as in Plate III, but it can be made binocular as figured, at an extra cost; as can also the Acme No. 3, and the Biological and Universal. It is one of the earliest instruments to which were applied several of the expedients just now termed the modern improvements of the microscope; and it presents, in combination with them the low square stage, and the small body of the continental style.
I. THE BIOLOGICAL STAND.
Of larger instruments, capable of utilizing all necessary accessories, and believed by the writer to be large enough for any histological work, Mr. Bulloch’s Biological Stand, represented in Plate X, was one of the first to assume substantially its present form. In this stand the tail—piece is made double, one portion carrying the substage and the other the mirror; an arrangement which is essential to the efficiency of this modern device, since the substage frequently requires to be in a position axial to the compound body, for the purpose of holding illuminating lenses or prisms, for instance, at the same time that the mirror is being used in an oblique position. The usefulness of the whole arrangement is impaired in such cases unless the different parts can be moved independently of each other.
J. THE UNIVERSAL STAND.
This stand, made by the Bausch and Lomb Co, is represented 1/3 natural size in Plate XI. It comprises the same general features as the one last named, but by a slight increase of distance between the stage and the table sufficient space is secured to admit the use of the largest illuminating or polarizing apparatus, etc., that is usually employed on the largest stands. In fact there is scarcely any of the accessory apparatus of the highest priced microscopes that cannot, with a few slight modifications in non-essential particulars, be easily and efficiently combined with this. This stand can he obtained as shown in the cut, in a very simple and inexpensive style; but it is capable of a much higher development. It has been constructed, for the use of the writer, with the addition of lengthening mirror bar, graduated draw-tube for use in micrometry and in drawing to scale at any desired amplification, centering adjustment to stage, and of the same substage moved vertically with rack and pinion and graduated fine adjustment screw with index point for use in measuring approximately the thickness of objects or cover-glasses. It is named by the makers the "Universal", from the belief that it is possessed of the working capacity of the most elaborate stands. The stage is well adapted to the use of a glass sliding stage and a mechanical stage moved in all directions by special mechanism can be added if desired.
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