Microscopes and Accessory Apparatus Part 2

=Stands.=

For the past thirty years division of labor has been employed to the utmost possible extent in the manufacture of our microscopes. This principle has been applied to our machinery as well as to our workmen, with the result that we have gradually acc.u.mulated a large plant of special machinery of the most accurate construction, each machine especially adapted to the manufacture of some particular part of our microscopes. By this development of mechanical appliances for microscope manufacture two ends have been attained:--The greatest accuracy and uniformity of construction of our microscopes has been made possible, while at the same time it has been possible to cheapen the cost of manufacture. Instruments which are the product of delicate machinery must always be more uniform, more accurate and should be less costly than those manufactured by hand.

In the following remarks we refer more particularly to the larger microscope stands of our manufacture and draw attention to those parts which should be present in every well equipped microscope.

The elements of these microscopes are:

1. =The foot and upright support with joint for inclination=, 2. =The stage=, 3. =The sub-stage, with condenser, iris diaphragm and mirror=, 4. =The body with the adjustments=, 5. =The tube, carrying eye-piece, nose-piece and objectives=.

1. =The foot and upright support= are solid and are of such weight and shape as to permit inclination of the body of the microscope to a horizontal position. The foot is horse-shoe shaped and is made to touch the table at three points, thus insuring stability even on a surface which is not entirely level. Inclination of the body of the microscope is permitted by a joint in the upright, which joint may be fastened in the larger stands by a set-screw operated by a lever. Stands Ia and IIb are also made with the English foot. Abundant s.p.a.ce is left under the stage for the various attachments of the sub-stage.

2. =The stage= of Stands A, I, Ia and II is round, revolving and centering. The centering arrangement consists of two small thumb-screws so situated at the sides of the stage as to control motion of the stage in all directions, thus to a limited extent serving the purpose of a mechanical stage.

=The other microscope= stands have square immovable stages, sufficiently large for general microscopic work. For the examination of very large sections two instruments are manufactured: the _Nebelthau_ sliding microscope (p. 50) and the stand after _Dolken_ (p. 52). The former is for magnifications up to 120 diam, whereas the latter can be used with any magnification.

3. =The sub-stage= carries a plane and concave mirror, the condenser and the diaphragm for regulating the illumination of the object.

=The Condenser= is so adjusted as to concentrate the rays of light about 2 mm above its surface, which is the average thickness of the microscopic slides, under an angle equal to the angular aperture of the highest power objective, which is about 120.

In the lower power objectives the angular aperture is to be reduced by the iris diaphragm.

To focus the Condenser properly it is adjustable by rack and pinion movement on Stands A, I, Ia, Ib, and by side screw on Stands II and IIa.

4. =The body= of the microscope carries the tube and is fitted with two adjustments for focussing; a coa.r.s.e adjustment and a fine adjustment.

The smooth working of these adjustments is one of the chief requirements of a good microscope.

=The coa.r.s.e adjustment= consists of rack and pinion and moves the tube of the microscope in a vertical groove with the least possible friction.

The teeth of the rack and pinion are set obliquely to the axis of the tube and are so adjusted that two teeth of each are always interlocked, thus avoiding all possibility of slipping or loss of motion in the movement.

[Ill.u.s.tration: Figure of the Micrometer-screw of the fine adjustment.]

=The fine adjustment= consists of a micrometer screw which moves the tube and arm of the microscope supporting the coa.r.s.e adjustment vertically upon a triangular column. This column is virtually a continuation upward of the upright support of the base of the microscope. Around the column is a broad collar so accurately fitted that it moves smoothly upon it with a minimum of friction and still without lateral motion, the movement being controlled by means of a micrometer screw at the top of the column. The head of this micrometer screw, a section of which is shown in the accompanying figure, is milled and is graduated in such a way as to indicate the exact degree of motion of the microscope tube which is accomplished by turning the micrometer screw, each division of the graduation corresponding to a motion of the tube through 1/100 millimeter, and a complete revolution of the screw corresponding to a motion of the tube through millimeter. The accuracy of this adjustment and the smoothness of its motion must be conceded to be a triumph of mechanical skill.

=Stands A.= and =I.= are fitted with a =new fine adjustment= device (one division on the micrometer screw corresponding to 1/1000 mm.) which is fully described on pages 25-26.

5. =The tube= of the microscope encloses a second tube, or draw-tube, which latter carries the eye-piece, and is so graduated as to indicate the exact length of tube in use at any time. The lower end of the tube has a thread into which the various objectives or a nose-piece screw.

Tube and objectives are provided with the so-called "Society screw".

=The nose-piece= has now become an almost indispensable part of a working microscope. It can, however, be used to best advantage only on such stands as are provided with a coa.r.s.e adjustment by rack and pinion.

Aside from the advantage derived from the rapid changing of objectives, which it permits, it is so accurately made and centered as to materially facilitate the focussing of the various objectives. It is only necessary to focus with the fine adjustment to obtain a view of the same microscope field which had been under observation before the change was made.

As it is necessary for this purpose that the objectives should be accurately adjusted to the nose-piece, it is very desirable that in ordering an instrument its nose-piece should be ordered at the same time if one is to be used, as subsequent ordering may necessitate the return of the stand and objectives to us.

=Stands A, I, Ia, Ib, II, IIa, IIb and III= are those which are best suited to fine microscopical investigations. Among them the physician and bacteriologist will find an instrument entirely suited to his particular needs.

=Stand III= is now provided with rack and pinion adjustment.

=Stands IV and V= are small instruments, which serve nevertheless many purposes where the more elaborate outfits are unnecessary. They make excellent laboratory stands for elementary courses in microscopy.

In =Stands IV and V= the coa.r.s.e adjustment is by means of sliding tube.

They are all provided with fine adjustment by micrometer screw.

=Stand VI= is provided with rack and pinion adjustment only. It has a large stage, and is particularly intended for searching for trichinae and for similar examinations where a very strong durable stand is desired and where the use of high power objectives is unnecessary. It may also be useful as an auxiliary stand for purposes of demonstration in laboratories.

=Stands III, IV, V, VI= have no joint for inclining the body.

=Stands A, I, Ia, Ib, II, IIa, IIb, III, IV= have mahogany cases (provided with a nickelled handle), in which the microscopes stand.

=Stands V and VI= are laid in mahogany boxes.

These cases are furnished with the microscopes without extra charge, when a =complete outfit=, including oculars and objectives is purchased.

Object clamps and test objects accompany every microscope.

The objectives to Stands A, I, Ia, Ib, II, IIa, IIb are in bra.s.s boxes; those for Stands III, IV, V and VI are in morocco cases.

=Illuminating Apparatus.=

=a. Illuminating Apparatus of Stands A and I.=

The apparatus includes the following parts:

Cylinder iris diaphragm.

Swing-out condenser.

Diaphragm carrier with iris diaphragm.

Plane and concave mirror.

The cylinder iris diaphragm comes into play when the condenser is swung out of position. To do this the diaphragm carrier is turned to the side as shown in the diagram, a small k.n.o.b is pressed, which liberates the condenser, and the latter is swung out to the side.

The regulation of the cylinder iris diaphragm is accomplished by means of a lever. Before the condenser is swung back into position the cylinder iris should be opened to its fullest extent. The lower iris diaphragm is for use in connection with the condenser only. It is regulated by means of a small k.n.o.b.

A horizontal rack and pinion arrangement permits oblique illumination, and a vertical rack and pinion permits adjustment of the whole sub-stage. By these means a most perfect control of the illumination of the object is a.s.sured.

Ground or colored gla.s.s discs may be inserted above the iris diaphragm if modification of the light is desired. =$30.--=

_This illuminating apparatus may also be fitted to Stands Ia and Ib._

[Ill.u.s.tration: Abbe's Illuminating Apparatus for Stand A and I.

Swing-out Condenser.

Cylinder Iris Diaphragm.]

=b. Illuminating Apparatus of Stands Ia and Ib= (p. 30, 32, 34).