In beginning work with the compound microscope, place the base of the microscope opposite your right shoulder, if you are right-handed; or opposite your left shoulder, if you are left-handed. Incline the body so that the ocular is on a level with your eye, if necessary; but if not, work with the body of the microscope in an erect position. In viewing the specimen, keep both eyes open. Use one eye for observation and the other for sketching. In this way it will not be necessary to remove the observation eye from the ocular unless it be to complete the details of a sketch.

Learn to use both eyes. Most workers, however, accustom themselves to using one eye; when they are sketching, they use both eyes, although it is not necessary to do so.

Open the iris diaphragm, and incline the mirror so that white light is reflected on the Abbe condenser. Place the slide on the centre of the stage, and if the slide contains a section of a plant, move the slide so as to place this specimen over the centre of the Abbe condenser. Then lower the body by means of the coarse adjustment until the low-power object, which should always be in position when work is begun, is within one-fourth of an inch of the stage. Then raise the body by means of the coarse adjustment until the object, or objects, in case a powder is being examined, is seen. Open and close the iris diaphragm, finally adjusting the opening so that the best possible illumination is obtained for bringing out clearly the structure of the object or objects viewed. Then regulate the focus by moving the body up or down by turning the fine adjustment. When studying cross-sections or large particles of powders, it is sometimes desirable to make low-power sketches of the specimen. In most cases, however, only sufficient time should be spent in studying the specimen to give an idea of the size, structure, and general arrangement or plan or structure if a section of a plant, or, if a powder, to note its striking characters. All the finer details of structure are best brought out with the high-power objective in position.

In placing the high-power objective in position, it is first necessary to raise the body by the coarse adjustment; then open the iris diaphragm, and lower the body until the objective is within about one-eighth of an inch of the slide. Now raise the tube by the fine adjustment until the object is in focus, then gradually close the iris diaphragm until a clear definition of the object is obtained. Now proceed to make an accurate sketch of the object or objects being studied.

In using the water or oil-immersion objectives it is first necessary to place a drop of distilled water or oil, as the case may be, immediately over the specimen, then lower the body by the coarse adjustment until the lens of the objective touches the water or the oil. Raise the tube, regulate the light by the iris diaphragm, and proceed as if the high-power objectives were in position.

The water or oil should be removed from the objectives and from the slide when not in use.

After the higher-powered objective has been used, the body should be raised, and the low-power objective placed in position. If the draw-tube has been drawn out during the examination of the object, replace it, but be sure to hold one hand on the nose-piece so as to prevent scratching the objective and Abbe condenser by their coming in forceful contact. Lastly, clean the mirror with a soft piece of linen. In returning the microscope to its case, or to the shelf, grasp the limb, or the pillar, firmly and carry as nearly vertical as possible in order not to dislodge the eye-piece.

Illumination

The illumination for microscopic work may be from natural or artificial sources.

It has been generally supposed that the best possible illumination for microscopic work is diffused sunlight obtained from a northern direction. No matter from what direction diffused sunlight is obtained, it will be found suitable for microscopic work. In no case should direct sunlight be used, because it will be found blinding in its effects upon the eyes. Natural illumination - diffused sunlight - varies so greatly during the different months of the year, and even during different periods of the day, that individual workers are resorting more and more to artificial illumination. The particular advantage of such illumination is due to the fact that its quality and intensity are uniform at all times. There are many ways of securing such artificial illumination, no one of which has any particular advantage over the other. Some workers use an ordinary gas or electric light with a color screen placed in the sub-stage below the iris diaphragm. In other cases a globe filled with a weak solution of copper sulphate is placed in such a way between the source of light and the microscope that the light is focused on the mirror. Modern mechanical ingenuity has devised, however, a number of more convenient micro lamps (Fig. 30). These lamps are a combination of light and screen. In some forms a number of different screens come with each lamp, so that it is possible to obtain white -, blue -, or dark-ground illumination. The type of the screen used will be varied according to the nature of the object studied.

Fig. 30. Micro Lamp.