Journal of the Royal Microscopical Society

the tube with a pencil, and the fly will soon show its head through the hole in the disc. The tube is then taken away, and the wool plugged up in the cone to keep the fly in its place. A pair of stage forceps, with the ends made hollow like a pair of gasfitter's pliers, can be used to hold the

cone.

Mr. Macer showed a living house-fly with this apparatus, at the November Conversazione, in a very effective manner.

(4) Photomicrography.

Nelson and Curties's Photomicrographic Camera.-At the November meeting of the Society Mr. E. M. Nelson read the following description of his photomicrographic camera (fig. 244) * :- -" Mr. C. L. Curties and myself have designed this camera in the hope of combining efficiency with simplicity. The points in its construction are as follows:--A board on indiarubber feet of sufficient length to take lamp, Microscope, and camera when fully extended. The usual chocks to hold the Microscope feet, and the fine-adjustment focusing-rod on the right-hand side of the board. The camera made of two square tubes of cardboard sliding one inside the other. Upright wooden ends to hold the cardboard tubes; these slide in grooves in the base board, and are fixed by clamping-screws. The front board has a brass nozzle to fit into the light-excluding cap on the Microscope. The back board is grooved to receive the focusing-glass and the double back. The lightexcluding cap is made of cardboard covered with leather, which is as efficient, and not so heavy, as the ordinary brass ones. The double backs are of iron; they are about one-sixth of the cost, and far smoother in their action, than mahogany ones. There is a fitting to hold diaphragms in the back.

The method of working is as follows:-The Microscope, inclined to a horizontal position, is placed in the chocks, the camera closed up, and slid back as far as it will go to the other end of the board. There will now be plenty of room between the camera and the Microscope for the eye to be conveniently placed to the eye-piece. The lamp, condenser, &c., are now centered in the usual manner, and a critical image of the object received by an ordinary eye-piece. When all the necessary adjustments are completed, the ordinary eye-piece is removed, and a projection eye-piece substituted for it. The camera, still closed, is now slid up to the Microscope, leaving sufficient distance between them to allow the hand to focus the eye-lens of the eye-piece. Next let a piece of paper be held up in the position the back will occupy when the photograph is being taken, and the diaphragm of the eye-piece focused, by means of the eye-lens, sharply upon it. The camera is now slid up to the Microscope, and the nozzle inserted in the lightexcluding cap. The camera is now extended to the required distance, and the object focused on the plate in the usual manner.

The following are a few hints in the use of the above camera :- It is not advisable to push magnifying power more than ten times the initial power of the objective. To this end the camera has been designed for use with Prof. Abbe's lower-power projection eye-pieces, as he recommends the lowerpower eye-pieces in preference to the higher when sufficient camera length can be obtained.

A plain glass screen is recommended in place of the usual ground glass. The best focusing-lens is an aplanatic lens of six power by Zeiss (Catalogue No. 127).

* Described ante, p. 661.

† As shown in the fig. these are round; they were subsequently made square on the suggestion of Mr. J. Mayall, junr., as being more serviceable in that form.

To find out the length of exposure, use a Warnerke's sensitometer, in conjunction with the table and directions in Mr. Bousfield's 'Guide to Photomicrography.'"

Photographing Series of Sections.*-Dr. W. His photographs serial sections with a magnification of 10-20 diameters with the following apparatus: A toothed bar carries at its front end a plate with the photographic objective Ob: a second plate, moved by a rack and provided with a central aperture, serves as object-carrier T: the two plates are united by bellows. The source of light is an Argand burner B, movable along the toothed stage. The light is concentrated by two plano-convex lenses L, with a

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diameter of 11.5 cm. and a focal distance of 8 cm. Diffuse light is avoided by the tin case Gh, in one side of which a broad valve or door is situated, in order to obtain access to the inclosed parts. The objectives used were a Steinheil's antiplanatic of 12 cm. focal distance or an aplanatic of 14 cm. The latter, though not so powerful as the former, gives a correcter and more definite image. Instead of a camera, the wall of the dark chamber W is used as a reception surface; the latter is divided into two halves and fitted with a door and shutter S. By means of S the light is thrown on or turned off the sensitized paper. The apparatus rests on a board Br which can be moved along the surface of the wooden stand G. This suffices for rough focusing. Finer focusing is obtained by moving the object-carrier T with a screw. Exact focusing is made by turning the objective, which works in a tube provided with a fine screw-thread. The sensitized paper is, if small, fixed down by small pegs; if large it must be fitted into a frame C, fastened to the wall. The image is first focused on a piece of white paper placed behind the glass plate of the frame, and, this done, the sensitized paper is introduced while the shutter S is closed. The paper employed is Eastman's silver bromide paper, which is sensitive enough to artificial light,

Arch. f. Anat. u. Physiol.-Anat. Abtheil., 1887, pp. 174-8 1 fig.).

and requires but simple manipulation. The length of exposure varies with magnification and the diaphragm; with Steinheil's aplanatic of 14 cm. focal distance, with diaphragm 4 for a magnification of 10 times, 6-8 minutes are required. Thin sections require longer than thick or deeply stained specimens. All the necessary details of manipulation are given with each packet of the Eastman's paper, but it may be mentioned that after exposure the paper is moistened with water and the image developed with acetate of potash and sulphate of iron. It is then washed in acidulated water, and having been fixed with hyposulphite of soda, is frequently washed, and the sheet is then dried. The time occupied in taking four slides with twenty-five sections each, magnified 10 times, is from an hour to an hour and a quarter.

In addition to giving an accurate copy of the sections, the method is most useful for reconstruction of the image, and if before cutting Kastschenko's definition planes are applied, the fine lines appear on every negative, and this renders the copies still more suitable and convenient for reconstruction purposes.

Ellis's Focusing Arrangement for Photomicrography.- Mr. John Ellis writes us:-"All the focusing arrangements for photomicrography have appeared so defective to me, that I venture to send a description and drawing of the one I use. The rod running the length of the camera carries

a loose arm, at the end of which is a roller, covered with indiarubber, which is made to revolve by an endless strap passing round a wheel upon the rod. The roller is kept in contact with the fine-adjustment screw of the Microscope by an indiarubber band attached to the base-board and the arm."

Nelson's Photomicrographic Focusing-screen.-This (the design of Mr. E. M. Nelson) is made by engraving the English and metrical scales, as well as a crossed diagonal, on the plane-glass plate which is used by nearly all photomicrographers. The engraving, which forms a convenient object to focus on, is a scale for measuring the magnifying power. The English scale is divided into inches, tenths, and half-tenths, and the metrical into cm. and mm. The scales are ruled horizontally, one inch apart, across the plate, one on either side of the cross made by the diagonals. The diagonals are not ruled at the points where they pass through the scales, in order that they may not interfere with the divisions.

DENAEYER, A.-Résumé de la conférence publique sur les procédés de reproduction

aux encres grasses des clichés photomicrographiques et des images d'objets scientifiques. Exposé d'un procédé nouveau de photolithographie, avec démonstrations

See this Journal, ante, p. 511.

pratiques. (Résumé of the public lecture on the processes of reproducing with printing inks photomicrographic clichés and images of scientific objects. Description of a new method of photolithography, with practical demonstrations.)

Bull. Soc. Belg. Mier., XIII. (1887) pp. 182–5 (1 pl.). HENSEN, V.-Ein photographisches Zimmer für Mikroskopiker. (A photographic room for microscopists.) Kölliker's Gratulationschrift, 1887, pp. 61-71 (1 pl.). KING, Y. M.—The Photomicrography of Histological Subjects.

Journ. of Micr., VI. (1887) pp. 205-16, from New York Med. Journ. MARKTANNER, G.-Bemerkungen über Mikrophotographie. (Remarks on photomicrography.) Phot. Corresp., 1887, p. 237.

(5) Microscopical Optics and Manipulation.

Microscopical Tube-length, its length in millimetres, and the parts included in it by the various opticians of the world.*-Prof. S. H. Gage read a paper with the above title to the Pittsburg Meeting of the American Society of Microscopists.

"In the construction of microscopic objectives, the corrections must be made for the formation of the image at a definite distance, or, in other words, the tube of the stand of the Microscope on which the objective is to be used, must have a definite length. Consequently, the microscopist must know and use this distance or microscopical tube-length' to obtain the best results in using the objective in practical work.

In order to obtain the exact distance in millimetres for which objectives are corrected, and the parts of the Microscope included in this distance or 'tube-length,' the following questions were submitted to all the opticians of the world whose addresses could be obtained:-1. For what 'tube-length' do you correct your microscopic objectives? Please give the length in millimetres or inches. 2. Please indicate on the diagram on the opposite page (fig. 247) exactly what parts of the Microscope you include in tubelength.' From nearly all precise and satisfactory answers were received, and I wish to express here my appreciation of their courtesy. The answers received are given below, and indicated on the accompanying diagram.

TABLE giving Length in Millimetres and showing parts included in TubeLength' by various Opticians.

Parts included in

'Tube-length.'