12. Extraordinary Fall of Rain.

On the 21st of October, 1817, (the day the hurricane commenced in the West Indies) at the Island of Grenada, with the wind west, and the barometer at 29.40, eight inches of rain fell in twenty-one hours, and the rivers rose thirty feet above their usual level. From the 20th of October to the 20th of November, seventeen inches of rain fell.

13. Magnetism applied as a Test for Iron.

The third Number of the Annales des Mines contains a paper by M. Haüy on the means of detecting iron in mineral, or other substances, by magnetism. Its presence is ascertained by the attraction of the substance, either immediately or after having been heated in the flame of a taper, on the magnetic needle, but in order to make the effect more sensible and evident, M. Haüy has taken advantage of the combined forces of the magnetism of the earth and of a bar magnet acting simultaneously on the needle.

The needle should be of excellent steel, and highly magnetic, its cap should be made of agate or rock crystal, and the point on which it moves very fine. If such a neeedle be left to itself it will stand parallel to the magnetic meridian, in consequence of the forces exerted on it by the magnetic poles of the earth, and if from any cause the needle is deflected from this line, the force exerted upon it to bring it back to its first position will be as the sine of the angle which the needle makes with the magnetic meridian. The power, therefore, which tends to return the needle to its first position, increases until it has passed through a quarter of a circle, and then decreases again, but the increase is in a decreasing ratio, and the decrease in an increasing ratio; and supposing the needle to be moved through 90° by nine successive additions of force, it would require the greatest addition, to move it from 0 to 10°, and the least to move it from SO to 90°; and then if the power which moved it from 80 to 90° carry it over that point, it would be more than sufficient to make it traverse the next quadrant, because the forces exerted by the earth's magnetism continually decrease.

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 85° to 90°, and afterwards 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. Hauy 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 arbitary 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 Potatoe.

Don Jose Pavon, the celebrated author of the Flora Peru. viana, who resided many years in South America, says, "The 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 Fe 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 country from Finland. It was found some years ago at the village of Ersby, near Abo.

It is of a green colour; is translucent and transparent. Its crystals are of various sizes, from an inch downwards. Its 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 gavity 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 constituents.

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 analysed. 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, and lost 40 per cent. It was infusible before the blow pipe. 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 Sates. 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