ARCANA OF SCIENCE.
Thunder and Lightning.
Conductors affixed to houses should always be pointed, and the point should be kept in a state of cleanliness, and the conductors should terminate in a moist stratum of earth, or in London it might safely be conveyed into the common sewer. It has been objected to the use of pointed conductors, that we invite the lightning to the point; and that is true to a certain extent, and in gunpowder mills the conductor should be placed at some distance from the building. The conducting rod should be of copper or iron, and from half to three-fourths of an inch in diameter, so as not to be readily forced. Its upper end should be elevated about three or four feet above the highest part of the building, and all the metallic parts of the roof should be connected with the rod, which should be continuous throughout. As regards the question of what is the safest situation in a thunder-storm, we should be pretty safe in the middle of a large room in bed; we should be pretty safe among the feathers, which are bad conductors; but as the bell-wires will conduct the electricity into the room, the bed should be removed from them. It would be well to stand at a distance from the chimney on a woollen rug, which is a non-conductor. When out of doors, I scarcely need to say, that you should never stand under a tree; the tree being moist, the electric fluid generally passes down between the bark and the substance of the tree, splitting it in all directions, and the lightning will pass to the best conductor near it; if any unfortunate animal should happen to be under the tree, it will be killed. The safest plan is to go toward the middle of the field, at a distance from any tree, and to stretch yourself out upon the ground, although this is not a very pleasant situation, especially in hard rain. During a thunder-storm, the earth is in a state of electricity as well as the clouds, and the light and heat which are produced at the explosion indicate the annihilation of the two electricities. Sometimes the discharge is only from cloud to cloud, sometimes from the earth to the clouds, and sometimes from the clouds to the earth, as one or other may be in the positive or negative state. The clouds are usually more or less electrical when the vapour, floating about in the atmosphere, is condensed, and the earth being brought into an opposite state of electricity by induction, a discharge takes place, when the clouds approach within a certain distance, and sometimes the electric cloud perches upon a hill, and then discharges itself. The electricity passes through the clouds in a zig-zag direction, and the undulation of the air which it produces is the cause of the noise which we hear, called thunder, which is more or less intense, and of longer or shorter duration, according to the quantity of air acted upon, and the distance of the place where the report is heard from the point of discharge. If the danger be great, we have seldom any opportunity to count the time which elapses between the appearance of the lightning and the report: electrical effects take place at no sensible time; it has been found, that a discharge through a circuit of four miles is instantaneous, whilst sound moves at the rate of about twelve miles in a minute. So that, supposing the lightning to pass through a space of some miles, the explosion will be first heard from the point of the air agitated nearest to the spectator; it will gradually come from the more remote parts of the course of the electricity, and, last of all, will be heard from the very extremity; and the different degrees of the agitation of the air, and the difference of the distance, will account for the different intensities of the sound, and its apparent reverberations and changes. If you can count from two to three seconds between the appearance of the lightning and the sound, there is seldom much danger; and when the interval is a quarter of a minute, you are secure.—Brande's Lectures.—Lancet.
New Crane.
A crane for raising weights, on an entirely new principle—that of the application of the lever, assisted by wedges, instead of the usual plan of wheel and pinion, for multiplying power—has recently been constructed at the West India Docks. The power of two men, with the patent crane, is stated to be capable of lifting from 2-1/2 to 3 times the weight lifted through the same space in a given time, by the best constructed cranes on the old principle of wheel machinery.
Etching on Ivory.
The usual mode of ornamenting ivory in black, is to engrave the pattern or design, and to fill up the cavities thus produced with hard black varnish. Mr. Cathery has much improved and simplified the process, by covering the ivory with engraver's varnish, and drawing the design with an etching needle; he then pours on a menstruum, composed of 120 grains of fine silver, dissolved in an ounce measure of nitric acid, and diluted with one quart of pure distilled water. After half an hour, more or less, according to the required depth of tint, the liquor is to be poured off, and the surface is to be washed with distilled water, and dried with blotting paper. It is then to be exposed to the light for an hour, after, which the varnish may be removed by oil of turpentine. The design will now appear permanently impressed on the ivory, and of a black or blackish brown colour, which will come to its full tint after exposure for a day or two to the light. Varieties of colour may be given by substituting the salt of gold, platina, copper, &c. for the solution of silver.—Trans. of the Society of Arts.
Geology.
Among the fossil bones lately dug from under the lava of the mountain of Boulade, in the neighbourhood of Issoire, in France, none have been discovered belonging to the human body. The same is the case in the other mountains of the vicinity. But, although there are no human bones, in several places, and especially in the mountain of Boutaresa, (which is not far from the mountain of Boulade,) pieces of wood have been discovered, buried under the ancient lava, which observers worthy of credit declare seem to have been fashioned by the hand of man, and to have been cut with a hatchet, although rudely, and as might be expected in the infancy of the arts. Did man exist then, at that remote period when elephants, lions, and tapirs, lived in Europe, with rein-deer and bears? This is an exceedingly difficult question, and one which hitherto does not, by any means, appear to have been satisfactorily resolved.—New Monthly Magazine.