NATURAL PHILOSOPHY. 139 



COPYING DRAWINGS BY GALVANISM. 



Marshal Yaillant has described to the Academy of Sciences, of Paris, a 

 mode of copying drawings devised by M. Defrancc, and perfected by Col. 

 Leveret. The process is as -follows: 



The drawing is made on transparent paper, and is laid, face downward, 

 upon a board, and fixed by tacks. Coats of gelatine are then applied with a 

 brush to the back of the drawing, so as to obtain a sheet of gelatine from. 

 TOO to "5 T o mc h thick- Upon this gelatine the drawing is traced with a sim- 

 ple point. A solution of gutta-percha in sulphuret of carbon is then applied 

 with a pencil, and the coatings repeated until it has also assumed a thick- 

 ness of about y JJ-Q of an inch. This will require at least thirty coats. When 

 the gutta-percha is sufficiently dry, a plate of copper is laid on it to give it 

 stiffness. The whole is then turned up, and the original drawing exposed. 

 This is easily removed, and then by delicate touches of a sponge dipped in 

 water, the gelatine is separated from the gutta-percha, which is rnctalized by 

 black lead. The plate is then electrotyped as usual. 



The Marshal declares that by applying this process to the six-sheet map 

 of Kabilie, they have obtained an economy of seven-eighths of the time, 

 and of six-sevenths of the expense. Academy of Sciences of Paris, Nov. 19, 

 1853. 



DETERMINATION OF THE VARIATION OF THE COMPASS. 



"We have before us a simple but very useful contrivance, the invention of 

 Captain Toovey, of the mercantile marine, for determining the true varia- 

 tion of the compass. It is a simple dial, inscribed with an inner and an 

 outer circle, having the quadrants and eight points of the compass worked 

 off on each. In the centre is fixed a gnomon, to the foot of which is at- 

 tached a movable hand that travels round the dial. This hand, in using the 

 instrument, is made to indicate the direction of the ship's head, and her 

 course. The dial is then placed in a horizontal position on the capstan- 

 head, the ship's side, the poop-rail, or any other convenient place. The 

 bearings of the sun are then ascertained, and the shadow cast by the gno- 

 mon indicates with accuracy the angle of variation of the compass, which 

 is read off on the inner or outer circle with perfect ease. The dial is fitted 

 with a movable sight for ascertaining the bearings of any object in the 

 heavens or on the horizon. London Engineer. 



CAST-IRON MAGNETS. 



M. Florimond, Professor at Louvain, has succeeded in making very good 

 magnets of cast iron, very highly tempered. The quality of the cast iron 

 for this purpose must be neither too fine nor too coarse, and the plates should 

 be at least three times thicker than the plates of steel usually employed. 



ON INCREASING THE POWER OF LOCOMOTIVES BY MAGNETIZATION. 



The following paper was read before the American Scientific Association, 

 by Mr. E. W. Serrell : 



The importance of increasing the power of locomotive engines without 

 adding to their weight, which is so destructive to the superstructure of rail- 

 ways, led me to attempt to magnetize the driving-wheels, to obtain addi- 



