Page:Popular Science Monthly Volume 33.djvu/668

668 Paris, for example, can be fixed for the moment in these splits, as an aid in tracing the railway lines and measuring the distances between the several cities. Laas d'Aguen, in 1847, invented a kind of map which could be reproduced by printing. Previous to his, MM. Pignier and Boher Keller impressed maps in relief on thick paper, in which the meridians and parallels were represented by fine threads, boundaries by round points, mountains by large oval points, and seas and lakes by striæ. This method was adopted by the Moon Society in England and by the British and Foreign Blind Association, the first of which published atlases of terrestrial and celestial maps. M. Kunz, of Illzach, and M. Abel Pifre, of Paris, have published some most excellent maps, the former of which are very cheap, and the latter, the best of their kind, high.

M. Ballu took up some years ago the idea of Sanderson's tablet, for making arithmetical calculations. It is composed of a plaque divided by prominent metallic lines into many little squares pierced by nine holes arranged in threes, and numbered from 1 to 9 (Fig. 5, No. 1, 1'). Pins may be inserted into these holes, the



rounded heads of which project above the surface of the plaque, and indicate the figures from 1 to 9, according to the number of the hole they occupy. The system is simple, but it takes a considerable time to learn it. In Taylor's tablet, the metallic plate is pierced with stellated octagonal holes, in which square pins with beveled ends are set, one of the ends being smooth and the