ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
527 
nect readily with the milled head of the fine-adjustment by means of a 
silk cord. 
We are requested to note that in the woodcut the apparatus appears 
reversed from right to left. 
(6) Miscellaneous. 
A Method of Drawing Microscopic Objects by the Use of Co- 
ordinates.* — Dr. Cooper Curtice writes: — “The method which I am 
about to detail is one that I found in use by Dr. George Marx, of the 
Division of Illustrations, in the U.S. Agricultural Department, when I 
first engaged studying animal parasites in 1886, but it was originated 
some eight years earlier, as he informs me. 
It is a method that has such obvious merits that I take pleasure in 
placing it before students of the Microscope, but I present it as a relater 
of a valuable method rather than of original work. Its simplicity, its 
cheapness, its accuracy, the ease with which a figure of any magnification 
or reduction may be made, and the rapidity with which a beginner adapts 
himself to its use, all serve to recommend it. 
A small glass slide, of the size of an eye-piece micrometer, or a disc 
ruled into squares, is inserted into the eye-piece, so that the lines seem 
to rest upon the object. Tracing-paper is placed over cardboard ruled 
into squares. The drawing is then made freehand, the various points 
located in a symmetical position with respect to the lines underlying 
the paper that they occupy in the apparently ruled image. The drawing 
made on the tracing-paper may then be either transferred to drawing- 
paper without reduction or be reduced by applying the same methods 
that produced the picture, and then be worked up. 
Dr. Marx prefers using the slide. It is ruled into squares 1 mm. on 
each side, every third line being slightly deeper, to make it prominent. 
I prefer for most uses the finder made by Zeiss. It is a circular disc, 
upon the centre of which are ruled tw 7 o sets of ten lines at right angles 
to each other, the lines being 5/10 mm. apart. The lines are very neatly 
ruled, and covered by a thin cover-glass cemented to it with balsam. 
It is apparent that the system has a wide application, so far as the 
magnifications to be attained are concerned. The equation giving the 
magnification is x - - X c, a being length of object, b the length of 
image, c the ratio of the image to the drawn figure. 
Suppose that the amplification of objective is 5 X ; that the lines 
on the eye-piece slide to 1/2 mm. apart, and those on the cardboard be 
6 mm., then x = 5 X 6 X 2, or 60, for the unit of the card squares is 
twice those of the eye-piece squares. 
To use a series of objectives, or of squares for the eye-piece and for 
the cardboard, are easy matters. A single glass ruled to half millimetres, 
made to fit a low-power eye-piece, is sufficient to try the plan. Card- 
boards, either of Bristol boards or heavy calendered Manilla paper, may 
be ruled into squares 3, 5, 7 mm., &c., until the student has all the 
combinations desirable. 
By adopting this plan of drawing figures, I have found that objections 
* Amer. Mon. Micr. Journ., xii. (1891) pp. 52-3. 
