Extracted from The Journal of the Royal Microscopical Society, 1882

Hartnack's Drawing Apparatus (His's Embryograph). [Zeitschr. f. Instrumentenk, i (1881) pp. 284-7 (1 fig )] Dr. E. Hartnack describes his new drawing apparatus, which is a modification of the embryograph of Professor His. He-writes:"It is desirable for many purposes of natural history to trace exact outline drawings with low magnifying-powers, and to be able to regulate the power so that it may be easy to pass from one scale to another. The drawing apparatus hitherto employed in microscopy (even with the use of low objectives) have hardly allowed the use of a power less than 20 ; moreover, although through the movement of the tube it was not impossible to obtain any scale desired, yet, at any rate, it was not convenient."

"A short time ago Professor W. His published [Anatomie menschlicher Embryonen, Leipzig, 1880] the design of a drawing-apparatus which allowed the power to be varied at will from 4 to 40. He combined the Oberhauser camera with a small photographic objective in such a manner, that both could slide backwards and forwards in movable sockets, on a bar 60 centimetres long, provided with a scale. The bottom of the bar bears the movable object-stage, and under this is a microscope mirror. A glass plate placed at the side of the apparatus acts as the drawing surface." This apparatus has been employed for years by Professor His, but I have endeavoured to give it a more compendious form, and at the same time to extend its magnifying power still more. In this I have succeeded by employing different objectives for the lower and higher powers, so that it was possible to reduce the height of the apparatus by a third."

The accompanying figure shows the apparatus (Fig. 68), S being a circular column, and T an angular bar, the latter divided into millimetres. G is the drawing plate placed on the box (38 x 22.5 x 9.5 cm.) in which the apparatus packs by separating the pedestal, column and bar, the stage, &c.

Professor His writes to Dr. Hartnack as follows as to the use of the apparatus: " Your form is thoroughly serviceable, and allows of correct and convenient working with powers of 4 to 70. According to your request I append some information as to its management. The regulating of the magnifying power is the first thing to be attended to by means of a scale divided into half-millimetres as an object. The stage must be placed in its highest position, and the objective and the prism moved until the image projected upon the glass plate shows the desired magnifying power.

For a power of 4, the stage must be pushed downwards 20 mm., and in order to take in the whole of the field of view with powers of 4 or 5 it must be unscrewed from its ring and the latter used as the stage.

"The aperture of the stage is only 20 mm; short or longsighted people should always use the same spectacles. When the desired power has been determined the object to be drawn is placed on the stage, and focussed only by moving the latter. In order to obtain a distinct image, the object must be in the same plane as the numbers and strokes of the scale were previously, and if this is obtained by unaltered position of the objective and prism, the magnifying power of the whole apparatus must remain the same as before, the distance of the drawing-surface from the objective remaining unchanged."

[Some general remarks follow as to testing the objectives, the regulation of the light, &c.]

"Opaque objects are best drawn in liquids. My chief object being to draw embryos, I have had unpolished hollow vessels of black glass or marble made, 5-20 mm. in depth; the embryos were covered with alcohol and a thin glass plate placed over them in such a manner as to exclude air bubbles. If it is necessary to keep the embryo in a given more or less depressed position, this can be done by using small strips of glass suitably bent."

"The above directions will perhaps suffice to assist the inexperienced in the use of the apparatus, and I only hope that others may find it, in the elegant and convenient form which you have given it, as useful as I have done."

For drawing microscopic objects the camera ludica will be found useful. This is a small glass prism attached to the eye-piece. The microscope is inclined horizontally, and the observer, looking into the prism, sees the object directly under his eye, so that its outlines may be drawn on a piece of paper placed on the table. Some practice, however, is needed for satisfactory results. For the upright stands of German and French microscopes, the camera lucida of Chevalier & Oberhäuser is available. This is a prism in a rectangular tube, in front of which is the eyepiece, carrying a small glass prism (c, Fig. 17), surrounded by a black metal ring. A paper placed beneath is visible through the opening in the ring, and the image reflected by the prism upon it can be traced by a pencil. It is necessary to regulate the light so that the point of the pencil may be seen.

While unsigned, this instrument conforms to the 1881 model first described by Edmund Hartnack, Potsdam. In this case however, the instrument is supported by a horseshoe style base. Hartnack based this design on the "embryograph" first used by the Swiss anatomist and embryologist Wilhelm His (1831-1904). As the name of the instrument implies, it was originally designed to allow the accurate drawing of embryos, but it is more generally useful for the drawing of any object at relatively low magnification.