Page:Popular Science Monthly Volume 8.djvu/265

Rh above it, and the temperature is thus prevented from falling as low as it otherwise would.

Trapping Wild-Turkeys.—There is a touch of cynic humor in a peculiar mode of trapping wild-turkeys in Virginia, as described by a writer in Forest and Stream. Having discovered one of the familiar haunts of the birds, the trapper digs a trench eighteen inches deep and about as wide, and four or five feet long, with a slope from the outer end deepening to the middle. A pen of fence-rails is now built, the first rail being laid across the middle of the trench; this is the width of the pen, and it has the length of two rails. It is built to the height of eight or ten rails and covered over with the same. Some grain is now scattered around and in the trench, and a large quantity within the pen. The turkeys get on the train of bait leading into the pen, and with heads down, eagerly picking up the grain, they go under the sill-rail in quest of food. Half a dozen or so will perhaps enter in thus, and then they find themselves imprisoned. They go round and round to find an exit, but it never occurs to them to look down, and thus they never find the passage through which they entered.

Rationale of the Welding of Iron.—The welding of iron and the regelation of water are very ingeniously traced to the same cause by Mr. M. Jordan. Faraday was the first to observe the phenomenon afterward called "regelation." By this term we imply that when two pieces of ice are pressed even very gently together, the temperature being just below zero, they at once become welded to each other. Of this Thompson offers the following explanation: For all bodies which, like water, have the property of diminishing in volume as they liquefy, pressure, which tends to bring the molecules closer together, lowers the temperature of fusion. Consequently, when two pieces of ice are rubbed against each other, fusion takes place between the surfaces in contact, at a temperature below zero. But as soon as the pressure ceases solidification is again produced, and the pieces are welded together. With iron, observes Mr. Jordan, the case is the same. The two pieces to be welded together are brought to a white heat, i. e., more or less near to the fusing-point. The repeated blows of the hammer, or the pressure of the rolls, lowers the point of fusion, causing a superficial liquefaction of the parts in contact, and thus welding the masses together; and this because, like water, iron dilates in passing from the liquid to the solid state. "The careful comparative study of these two bodies," adds Mr. Jordan, "even though at first sight apparently so dissimilar, cannot fail to furnish results of great interest to the metallurgist. The work of the puddler is also based upon the same phenomenon as that of welding. When the puddler forms his ball in the furnace, it is done by rolling together or aggregating the crystals of iron as they form in the mass of melted iron and slag. In other words, the semi-fused crystals are welded or regelated together by the mechanical action of the puddler."

Propagation of Waves in Liquids.—At a late meeting of the Paris Physical Society, M. Marey exhibited certain apparatus which he has employed in studying the propagation of waves in liquids. His method consists in producing, at a given point in an India-rubber tube filled with water, a sudden compression or dilatation, either by pressing on the walls of the tube, or by means of a piston. Small clips arranged along the tube at equal distances from each other signal the passage of the wave of compression or dilatation to a registering apparatus. In this way M. Marey has found that the velocity of the waves decreases with the size and increases with the elasticity of the walls. The density of the liquid has also some effect, but this is not of sufficient importance to be taken into account in applying this method of observation to physiology.

Restoration of Faded Writings.—Very often paper and parchment documents are illegible owing to the ink with which they were written having faded. The Revue Industrielle gives a very simple method of restoring to the ink its color. It is as follows: First, wet the paper and then pass over it a brush dipped in a solution of ammonia sulpho-hydrate. The writing quickly reappears, the characters being of a very deep