COMPOUND See also:

• MICROSCOPE (Gr. µucp6s, small, asenreiv, to %view)

For example, the real image may be recorded on a photo-graphic See also:

• PLATE

But even with such moderate magnification as these See also:

• INSTRUMENTS

Weak systems act like photographic objectives. In this case the optical tube length may be altered within fixed limits without spoiling the image; at the same See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

The image viewed through the eyepiece appears then to the observer under the See also:

• ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

If this value of y be inserted in equation (5), we obtain the magnification number of the compound microscope: — N =tan w"/ tan w=Ol/fi'fa =Vl. (6) The magnification number increases then with the optical tube-length and with the diminution of the focal lengths of objective and eyepiece. As with the simple microscope, different observers see differently in the same compound microscope; and hence the magnification varies with the power of See also:

• ACCOMMODATION (Lat. accommodare, to make fit, from ad, to, cum, with, and modus, measure)

See also:

• BOULANGER
• BOULANGER, GEORGE ERNEST JEAN MARIE (1837-1891)

With powerful systems, object-points lying quite near the plane focused for would be represented by such large dispersion circles that practically only the points lying in one plane appear simultaneously See also:

• SHARP, GRANVILLE (1735-1813)
• SHARP, JAMES (1618-1679)
• SHARP, JOHN (1645-1714)
• SHARP, RICHARD (1759-1835)
• SHARP, WILLIAM (1749-1824)
• SHARP, WILLIAM (1856-1905)

The size of the imago on the focal plane is always equal to its actual size, and is See also:

• INDEPENDENT

Whether the entrance pupil be before or behind the object, in general its position is such that it lies not too near the object, so that the principal rays will have in the object space only trifling inclinations towards one another or are strictly parallel. This is specially important, for otherwise pencils from points placed somewhat later-ally to the, axis arrive with diminished aperture at the image. We see from fig. 13 that the objective's exit pupil P'Pi' is portrayed by the positive eyepiece, the image P"Pi" limits the pencil proceeding from the eyepiece. This image P"Pl" is then the exit pupil of the combined system, and consequently the image of the entrance pupil of the combined system. As the exit pupil P'Pi' for the objective lies before the front focus of the eyepiece, generally at some distance and near the objective, the eyepiece projects a real image from it behind its image-side focus, so that if this point is accessible it is the exit pupil P"PI". If, e.g. in the object-space the objective has telecentric transmission, the exit pupil must coincide with the back focal plane of the combined system, and it always lies behind the image-side focus of the eyepiece. The exit pupil, often called Ramsden's circle, is thus accessible to the observer, who by See also:

• HEAD (in 0. Eng. heafad; the word is common to Teutonic languages; cf. Dutch hoofd, Ger. Haupt, generally taken to be in origin connected with Lat. caput, Gr. KerbOvi7)
• HEAD, SIR EDMUND WALKER, BART
• HEAD, SIR FRANCIS BOND, BART

The pencils producing the real image are very much more acute, and their inclination is the smaller the stronger the magnification. The eyepiece, which by means of narrow pencils represents the relatively large real image at infinity, transmits from all points of this real image parallel pencils, whereby the inclination of the principal rays becomes further increased. The point of intersection, i.e. the centre of the exit pupil, is accessible to the eye of the observer. In the case of the negative eyepiece, on the other hand, the divergence of the principal rays through the eyepiece is also further augmented, but their point of intersection is not accessible to the eye. This property shows the superiority of the collective eyepiece over the dispersive. The increase of the inclination of the principal rays, which arises with the microscope, influences the See also:

• PERCEPTION (from Lat. percipere, to perceive)

The result must be that the field of view exhibits a sharp border. In the case of the dispersive eyepiece, on the contrary, no sharply limited field can arise, but vignetting must occur. See also:

• ILLUMINATION

A view taken under water from the point 0 (fig. 18) See also:

• SEES

In immersion-systems of such considerable aperture no medium of smaller refractive index than the immersion liquid may be placed between the surface of the front lens and the object, as otherwise total reflection would occur. This is especially in-convenient in the case of the a-bromnaphthalene immersion. As the embedding and immersing liquids must have equal refractive indexes, one must use a-bromnaphthalene for embedding; but this substance destroys organic preparations, so that one can employ this immersion-system only for examining inorganic materials, e.g. See also:

• FINE