Page:Principles of Microscope.djvu/22

xvi " and the "derivative" pattern (vide p. 8, Exps. 1 and 2, and footnote).

f. Glass spherule delineated by a dark outline upon a blue field. The object is mounted in water and is illuminated by narrow-angled beams which have been transmitted through the central area of the parti-coloured stop shown on Plate I, Fig. E, 3. The outline appears yellowish by colour-contrast when viewed through the covering tissue-paper (vide pp. 8-9 and p. 21, Exps. 4 and 6).

g. Glass spherule delineated by a dark outline upon a red field. The object is mounted in water and is illuminated by narrow-angled beams which have been transmitted through the peripheral area of the parti-coloured stop, shown in Plate I, Fig. E, 3, placed under a narrow substage diaphragm. The outline appears greenish by colour-contrast when viewed through the covering tissue-paper (vide pp. 8-9).

h. Glass spherule delineated by a red margin on a blue field. The object is mounted in water and is illuminated by wide-angled beams which have been transmitted through the parti-coloured stop placed centrally under a widely-open focussed condenser.

i. Semi-diagrammatical representation of a piece of blotting paper of which one half (the left half) is mounted in oil, while the other (right) half is mounted in air, the whole being illuminated by narrow-angled beams. On the left side, owing to the abolition of refraction and reflection by the filling in of the interstices of the paper by oil, the preparation has become transparent and the fibre of the paper has been rendered invisible. On the right side, where the interstices of the paper are filled in with air, refraction and reflection are preserved, with the result that the preparation is opaque and that the constituent fibres are delineated by hard dark outlines (vide pp. 29-30, Exps. 1-7).

j. Representation of the same object similarly mounted and similarly illuminated except in the respect that the light has been transmitted through a red light filter (vide pp. 29-30, Exps. 1-7).

k. Glass wool delineated by dark outlines upon a blue field. The filaments are here mounted in water and are illuminated by narrow-angled beams transmitted through a blue light filter (as shown in Plate XI, Fig. 2) and are viewed with a narrow-angled objective. The dark outlines appear yellow by colour contrast when viewed through the covering tissue-paper (vide pp. 8-9 and p. 177, Exp. 2).

l. Glass wool seen against a purple ground. The filaments are here mounted in water and are illuminated by wide-angled beams furnished by a fully open condenser and a parti-coloured stop (as shown in Plate XI, Fig. 1), and are viewed with a wide-angled objective (vide p. 210, Exp. 2).

m. Glass wool delineated by red outlines on a blue field. The filaments are here mounted in water, are illuminated by wide-angled beams furnished by a fully-open condenser and a parti-coloured stop (as shown in Plate XI, Fig. 1), and are viewed with a narrow-angled objective (vide p. 210, Exp. 2, and p. 155, Exp. 2). The red outlines, when viewed through the covering tissue-paper, appear yellowish by colour contrast to the blue field.

PLATE III (facing page 22).

a. A film preparation of blood in which the elements are delineated by dark outlines upon a bright field. (Dark outline picture.) The