4. Gelatine 1 gramme, glycerine à 30° 4 grammes, water 2 grammes. (Kwaysser and Husak.)
Fig. 876.—The chromograph.
The “mixture” is shaken until it cools to the point of thickening, and then poured into a zinc vessel. The kaolin or the sulphate of baryta makes the composition white. It can be treated again with gelatine and molasses employed for printing rollers. When the proofs have been taken from the frame the surface may be rubbed with a damp sponge, and then it will be ready for use again immediately. The introduction of dextrine facilitates the cleansing of the surface plate.
The Campylometer.[42]
This instrument, constructed by Lieutenant Gaumet, is very easily carried in the pocket, and by a very simple process gives (1) the length of any line, straight or curved, traced on a map or plan; (2) the actual length corresponding to a “graphical” length on maps of the scale of 1/80000 or 1/100000, or on maps which are multiples of these numbers.
The instrument consists of a toothed disc, the circumference of which is dentated exactly in five centimètres. The faces of this disc each carry a system of divisions; one is divided into four parts, the other into five. The circumference of the disc (5 centimètres) corresponds to the 4 kilomètres of the scale of 1/80000, and to 5 kilomètres of that of 1/100000. The division 1/40 of the disc in the former scale measures 100 mètres, and is in it the same as 1/50 of the other scale.
Fig. 877.—The campylometer.
The toothed disc moves upon a micro-metric screw, the markings of which are 0·0015 of a mètre, and a small “rule” or “reglet” carries equal graduations, as the screw representing lengths so follow:—