FILTERING APPARATUS.
(To the Editor of the Mirror.)
A A. The Pot. B B. The Triangular Board. C. The Cover. D. Vessel to receive the Filtered Water.
E. Dotted Line, showing the Proportion of Charcoal and Sand.
Herewith I send you an outline drawing of an economical filtering apparatus, suitable for the use of any dwelling. Its construction is perfectly simple, and at the cost of a few shillings in its erection. The pot consists of an unglazed inverted vessel, manufactured at potteries for the use of sugar-bakers, and placed through a hole in a triangular board, resting upon two ledges, occupying a corner in a kitchen or any other apartment. In the inside of the pot a bushel of the whitest sand is to be introduced; which sand, after being washed in a clean tub with about three changes of water, to dissolve and clear away the clayey matter, is to be mixed with half a peck of finely-bruised charcoal. This will fill about one-third of the pot; but before the sand is placed in the vessel, the small hole at the bottom of the pot should have an oyster-shell placed over it, with the convex side uppermost, to prevent the sand washing through. This filters foul water perfectly pellucid and clear very quickly, as I have seen its effects for years with the most perfect success. When the sand becomes foul by time, it can be taken out and washed, or fresh materials can be repeated; great care should be observed not to put more water in the pot than your vessel underneath will receive.
JNO. FIELD.
Effects of Lightning.
The analogy between the electric spark, and more especially of the explosive discharge of the Leyden jar, with atmospheric lightning and thunder, is too obvious to have escaped notice, even in the early periods of electrical research. It had been observed by Dr. Wall and by Gray, and still more pointedly remarked by the Abbé Nollet. Dr. Franklin was so impressed with the many points of resemblance between lightning and electricity, that he was convinced of their identity, and determined to ascertain by direct experiment the truth of his bold conjecture. A spire which was erecting at Philadelphia he conceived might assist him in this inquiry; but, while waiting for its completion, the sight of a boy’s kite, which had been raised for amusement, immediately suggested to him a more ready method of attaining his object. Having constructed a kite by stretching a large silk handkerchief over two sticks in the form of a cross, on the first appearance of an approaching storm, in June 1752, he went out into a field, accompanied by his son, to whom alone he had imparted his design. Having raised his kite, and attached a key to the lower end of the hempen string, he insulated it by fastening it to a post, by means of silk, and waited with intense anxiety for the result. A considerable time elapsed without the apparatus giving any sign of electricity, even although a dense cloud, apparently charged with lightning, had passed over the spot on which they stood. Franklin was just beginning to despair of success, when his attention was caught by the bristling up of some loose fibres on the hempen cord; he immediately presented his knuckle to the key, and received an electric spark. Overcome with the emotion inspired by this decisive evidence of the great discovery he had achieved, he heaved a deep sigh, and conscious of an immortal name, felt that he could have been content if that moment had been his last. The rain now fell in torrents, and wetting the string, rendered it conducting in its whole length; so that electric sparks were now collected from it in great abundance.
It should be noticed, however, that about a month before Franklin had made these successful trials, some philosophers, in particular Dalibard and De Lors, had obtained similar results in France, by following the plan recommended by Franklin. But the glory of the discovery is universally given to Franklin, as it was from his suggestions that the methods of attaining it were originally derived.