In order to take advantage of this circumstance, let the needle be influenced only by the earth's magnetism, it will stand parallel to the magnetic meridian; then if the south pole of a bar magnet be approached towards the similar pole of the needle, the bar being in a line with the needle, a repulsion will take place, and the needle will deviate until the repelling power of the bar and the attractive force of the earth on it, are equal to each other. This may have set the needle at an angle of 30° with its meridian; then by approximating the bar, the effect belonging to it will be increased, and the direction of the needle will become more oblique. By adjusting the bar in this way, the needle may be placed and retained in a position very nearly at right angles with its first direction; and then as the power of the earth on the needle increases but very little from the 80° or 859 to 90°, and afterward diminishes, a small force will make it pass the 90°, and once beyond that point it will continue to move until its position is completely reversed. The time of applying a mineral or other substances supposed to contain iron to the needle, is then when it is nearly at right angles with the magnetic meridian; because an effect will be produced there by a force many times smaller than that necessary to produce a similar effect on a needle uninfluenced, except by the earth's magnetism. M. Haüy found that in this way effects were produced on the needle by bodies that in common circumstances appeared to have no action, as hæmatite, the carbonate, phosphate, chromate, and arseniate of iron, ferriferous carbonate of lime, garnet, peridot, &c. and he observes that this extension of character by means of double magnetism, may be usefully employed in the description of ferriferous minerals. As the garnet and peridot are the only gems of their own colour that have been observed to affect the needle, this character may be combined with their physical properties to distinguish them, and other stones, when cut into arbitrary forms by the lapidary. 14. Morrichini's Experiment in Magnetism. Mr. Playfair appears to have made with success whilst at Rome, the doubtful experiment of Dr. Morrichini on the communication of magnetism to a steel needle by the violet rays of the solar beam. The arrangement of the apparatus was in the old form, and the time required to produce the effect was 55 minutes. III. NATURAL HISTORY. § 1. BOTANY. 1. Native country of the Potato. "The Don Jose Pavon, the celebrated author of the Flora Peruviana, who resided many years in South America, says, Solanum tuberosum grows wild in the environs of Lima, in Peru, and 14 leagues from Lima, on the coast. I have also found it wild in the kingdom of Chili." The Indians cultivate it in great abundance in Peru and Chili, and call it Papas. It is said also to have been found in the forests near Santa Fè de Bagotá. 2. Alder-Tree. The Earl of Carlisle has an alder-tree now growing on his estate in Cumberland, which, about three feet above the ground, is more than nine feet in circumference. His Lordship has also in Geltsdale Forest, three distinct species of trees growing out of one common solid trunk. A common ash, a mountain ash, and an alder. §2. MINERALOGY, GEOLOGY, &c. 1. Pargasite, a new Mineral. A new mineral, called Pargasite, has been sent to this coun try from Finland. It was found some years ago at the village -of Ersby, near Abo. Its Its It is of a green colour; is translucent and transparent. crystals are of various sizes, from an inch downwards. form is an octohedron, with a rhomboidal base. It has three cleavages. It is harder than fluor spar, but is scratched by quartz. It also scratches glass. Specific gravity 3.11. It melts before the blow-pipe into a mass of a pearly white lustre. The following are given as the proportions of its consti 2. Instrument to distinguish Minerals. Dr. Brewster has lately constructed an instrument for distinguishing the precious stones from each other, and from artificial imitations of them, even when they are set in such a manner that no light can be transmitted through any of their surfaces. The same instrument may be employed to distinguish all minerals that have a small portion of their surface polished either naturally or artificially. The application of the instrument is so simple, that any person, however ignorant, is capable of using it. 3. Silicated Hydrate of Alumine. A combination of alumine, silex, and water, has been found native by M. Lelièvre, and lately analyzed. It was discovered in 1786, in the gallery of a lead mine, on the bank of the river Oo, in the Pyrénées. It is opaque and white, but sometimes slightly yellow or green. In its natural situation it was soft, and perpetually moistened by a small stream of water. When dry, the fracture was resinous. It barely scratched carbonate of lime, adhered to the tongue, and put into water absorbed about of its weight. Heated, it became friable and light, It was infusible before the blow-pipe. and lost 40 per cent. When acted on by acids, it assumed a gelatinous appearance. An analysis by M. Berthier gave, It has been named Silicated Hydrate of Alumine, (alumine hydratée silicifère.) 4. Native Copper. An enormous mass of native copper has been found in North America by M. Francis le Baron, of the United States. It was discovered in the bed of the river Onatanagan, and measures 12 feet round at one end, and 14 feet at the other It is supposed to have been detached from some distant source, and brought by the force of the waters to its present situation. The pieces that have been taken from it appear to be very pure; they are extremely ductile, malleable, and capable of being highly polished. 5. Fossil Bone of a Whale. Part of the jaw-bone of a whale was dug up a short time since, in Roydon gravel pit, near Diss. It measured 20 inches in girth, but was not above nine inches long. The outside was penetrated by lapideous matter, but the inside was similar in every thing to recent bone, except in the colour, which had been given it by the stratum in which it lay. Its present form and appearance are attributed to the attrition it is supposed to have suffered at former times. The ends are so worn that they seem rather artificial than natural. 6. Remains of a Mammoth. A fisherman of Philipsbourg, on the Rhine, lately drew up in his net the foot and the omoplate of a mammoth. These curious remains were sent to the King of Baden's Cabinet of Natural History at Carlsruhe. 3. MEDICINE, &c. 1. Bite of the Adder. Dr. Leslie, in a communication to the Medical Journal, describes a case in which ammonia was successful in preventing the effects of the bite of an adder. Travelling in the North of England, he stopped to give assistance to a poor man who, having laid down on the grass to sleep, had been bitten. From experience of the beneficial effects of ammonia in India, in cases of the bites of different snakes, Dr. Leslie procured some spirits of hartshorn, and gave about a drachm of it, mixed with about half an ounce of gin, and a little water. The effect was very sudden. In ten or fifteen minutes the patient's eyes became more bright, his pulse fuller and stronger, and his countenance altogether more cheerful; and by the repetition of the same dose as above stated, in about the space of an hour and a half, he appeared perfectly recovered. Another dose was left to be taken at ten o'clock at night, and in the morning he said he was quite well, except a little numbness and weakness in the arm; the third day after he returned to his work. 2. Cure for the Hydrophobia. Dr. W. Rittmeister, of Powlowsk, Finland, has collected together a number of striking cases, and also several authorities, by which he endeavours to prove that blood when drank is a remedy for the hydrophobia, even when the symptoms have become very marked. When a man or an animal has been bitten by a rabid dog, wolf, or other creature, it is the custom in those parts to kill the diseased animal and give its blood to drink to those that have been bitten; they remain in health, and the wounds are treated in the common way. It is further said, in a letter from Dr. Stockman, in White Russia, to Dr. Rittmeister, that the blood of the person or |