The centre of a small circular iron plate is placed in the line of the attraction of the ship's iron, and at a proper distance behind and below the pivot of the compass needle, the position of this line having been ascertained previously to the ship's leaving port, an operation which will be greatly facilitated by a table for this purpose, prepared by Mr. Barlow. When this is done, the needle will remain active and vigorous in the polar regions, and will direct itself in the true magnetic meridian, in whatever part of the world the ship is placed. This effect of Mr. Barlow's invention has been experimentally established between the 61° of south latitude and the 81° of north latitude, by the accurate observations of Lieutenant Foster, and by other naval officers. There are few scientific inventions of modern times more truly beautiful in principle, and more useful in practice, than this of Mr. Barlow's.

13. Mr. Scoresby's New Experiments on Magnetism.-Mr. Scoresby had formerly shown, that bars of steel could be rendered highly magnetic by hammering them in a vertical position, with the lower end resting upon a poker or rod of iron. This process, however, he has greatly improved by hammering the steel bars between two bars of iron, three feet in width and one foot in length. The steel bars were the eighth part of an inch in diameter.

When only one bar of iron was used, a steel wire, six inches long, lifted a nail weighing 186 grains; but when two bars of iron were used, the wire lifted 326 grains. When the new process was employed with an iron bar eight feet long, a steel wire six inches long lifted 669 grains, or four times its own weight.

Mr. Scoresby's theory of this process is, that percussion on magnetizable substances in mutual contact inclines them to an equality of condition, in the same manner as all bodies of different temperatures tend to assume the same temperature when in contact. The two great iron bars being made magnetical by position, the interposed bar of steel will therefore, when thrown into a state of vibration by percussion, receive a portion of their magnetism. In like manner a magnet, when struck in the air with a piece of flint, or upon a body of inferior magnetic quality, will have its magnetism diminished.

14. Magnetic Variation near Littakun.—Mr. Burchell found, by a very accurate observation made nearly in 24° 15′ of East Long. and 27° 20′ of South Lat. that the magnetic variation was 27° 7′ West, a result which coincides nearly with that given in Hansteen's Chart and Tables. See Burchell's Travels, vol. ii. p. 325. Lond. 1824.

ELECTRICITY.

15. Dr. Hare's Single Leaf Electrometer.—This instrument is represented in Plate I. Fig. 10, which is an electrometer, with a single leaf suspended from a disc of zinc, six inches in diameter, which constitutes the top of the instrument Opposite to this single leaf is a ball, supported on a wire, which may be made to approach the leaf, or recede from it, by means of a screw. Above the instrument is seen a disc of copper, with a glass or metal handle. The electricity produced by the contact of copper and zinc is rendered sensible in the following manner. Place

the disc of copper on the disc of zinc, (which forms the canopy of the electrometer;) take the micrometer screw in one hand, touch the copper with the other, and then lift this disc from the zinc. As soon as the separation is effected, the gold leaf will strike the ball, usually, if the one be not more than of an inch apart from the other. Ten contacts of the same discs of copper and zinc will be found necessary to produce a sensible divergency in the leaves of the condensing electrompeter. In the figure above referred to, AB is the copper disc, CD the zinc disc; a the gold leaf, b the ball, and mn the micrometer screw and scale for regulating and measuring the distance between the ball and leaf in hundredths of an inch, and HF the wooden stand to which the glass foot is secured.-Professor Silliman's Journal, vol. vii. No. ii. P. 351.

ELECTRO-MAGNETISM.

16. Aurora Borealis imitated by an Electro-Magnetic Experiment.—M. de Chevalier de Nobili, of Modena, the author of this experiment, took a large metallic wire, covered with silk, and coiled it up so as to form a spiral plate, with 24 turns, the wire of one turn being always in contact with the adjacent one. When a weak electrical discharge is made to pass through this spiral plate, a light is seen to proceed from the centre of all the spires. It resembles artificial fire, and is very distinctly visible without darkening the chamber in which the experiment is made. When the wire is coiled up in a rectangular shape, a very faint light is seen. M. Nobili considers this last as the ordinary electrical light, and the first as electro-magnetic, as it is displayed only in the case when electricity exerts a magnetic influence. M. Nobili has announced a work entitled Questions sur Magnetisme, in which he discusses all the recent discoveries in that science. See Bibliothèque Universelle, Jan. 1824, P. 39.

METEOROLOGY.

17. Differences in Thermometers at low Temperatures. During the late arctic expeditions, Captain Parry found, by comparing ten thermometers, three of which contained mercury, and seven alcohol, that the difference of their indications was no less than 7 lying between -224° and 30. Two of these which indicated the mean of the whole were taken for use. At higher temperatures, the difference was found to be very inconsiderable.-Captain Parry's Second Voyage, p. 132.

II. CHEMISTRY,

18. On the Combustion of Iron by Sulphurous Vapour.-Professor has observed, that if a gun barrel be heated red hot at the bu and a piece of sulphur thrown into it, a jet of ignited sulphur pour will issue from the touch-hole, when the mouth of the b closed with a cork, or when it is blown into. He found that a of iron wire, exposed to this jet, will burn as if ignited in oxy and will fall down in the form of fused globules, in the state o sulphuret. When hydrate of potash is exposed to the jet, it into a sulphuret of a fine red colour.-Dr. Hare's Letter to i Silliman.

19. Dr. Hare's method of impregnating water with iron.—If we place a few pieces of silver coin alternating with pieces of sheet iron in water, it will soon acquire a chalybeate taste, and a yellowish hue, and in twentyfour hours flakes of oxide of iron will appear. Hence if we replenish with water a vessel in which such a pile is placed, after each draught, we may have a competent substitute for a chalybeate spring.

Clean copper plates alternating with iron, or a clean copper wire entwined on an iron rod, would produce the same effect; but as the copper, when oxidated, yields an oxide, it is safer to employ silver.-Dr. Hare's Letter to Professor Silliman.

11. NATURAL HISTORY.

MINERALOGY.

20. Hyalosiderite, a new mineral species.—This mineral occurs chiefly in small crystals belonging to the prismatic system of Mohs, their form being in most cases that of a diprismatic combination, two opposite angles of which are truncated by a single plane, nearly like Fig. 30, Plate III. without the faces P. The inclination of b upon the adjacent face b' is =99° 22′, of ƒ on ƒ'=77° 50′, of b on d=130° 19′, of ƒ on d=151° 5% The edges between b and b' are sometimes replaced by a single face, or by the faces of another prism of 121° 0'. The surface of the crystal is smooth; but the crystals themselves are often imperfectly formed, and occur also in the shape of grains loosely coherent. Cleavage indistinct, parallel to d. Fracture small, conchoidal. Lustre vitreous, on the surface a metallic appearance. Colour reddish, or yellowish brown, with a brass-yellow or gold-yellow tarnish on the surface. Translucent on the edges, with a hyacinth-red, or wine-yellow colour. Streak of a cinnamon colour. Hardness 5.5 (between Apatite and Felspar.) Specific gravity=2.875.

Hyalosiderite was discovered by Dr. Walchner of Freiburg, in Breisgau, and recognised as a particular species by himself and by Professor Hausmann, of Gottingen. It occurs on the Kaiserstuhl, in Breisgau, near the village Sasbach, in a basaltic amygdaloid of a reddishbrown, or liver-brown colour, and is accompanied with augite and bitter

spar.

The crystals of Hyalosiderite become magnetic if gently heated to blackness. At a higher temperature they melt into a globule, which is attracted by the magnet. With borax they yield very readily a transparent glass-coloured green by iron, varying in intensity according to the quantity of the mineral employed: it becomes black and opaque if the borax be saturated with it. With salt of phosphorus it leaves a skeleton of silica. The glass itself is greenish, and becomes colourless on cooling. With tin the glass of borax, containing a small portion of the mineral, becomes of a slight but beautiful green when cold.

Dr. Walchner gives a comparative chemical analysis, 1. Of hyalosiderite; 2. Of an iron slag from the Dax iron works in the Pyrenees, specific gravity =3.700; 3. Of an iron slag from Bodenhausen, in the Hartz, specific gravity 3.520; 4. Of a crystallized slag, from Lautenthal in the Hartz, described by Mr. Hausmann, specific gravity 3.870;

and 5. Of a mineral called volcanic iron-glass by Karsten. The last of these analyses is by Klaproth.

The iron slags appear, therefore, to consist principally of silicate of iron, part of the iron being replaced by magnesia in the hyalosiderite. Dr. Walchner moreover indicates an exact identity between the forms of crystallization of the two substances, at least in so far as measurements not perfectly accurate would allow him to judge. Notwithstanding these observations, the vast difference between the degrees of specific gravity, being below 2.9 for the one, and above 3.5 for the other, even though all their remaining properties should be found to be identical, will prevent them from being considered as belonging to one and the same species. From the analogy between the iron slags and the hyalosiderite, Dr. Walchner concludes that the rock in which it occurs must be of volcanic origin. The name of the mineral, from años, glass, and oíèngos, iron, has been suggested to him by its properties and composition. (From Schweigger's Neues Journal fur Chemie, &c. 6. ix. p. 65.)

21. Hopeite, a new mineral.-Form prismatic. Fundamental form a scalene four-sided pyramid of 139° 41′; 107° 2′; 86° 49′, Plate III. Fig. 29, in which the ratio of the three lines A M: MB: MC = ¢ is 14.443: 1.493. Combination observed similar to Plate

VIII. Fig. 6.

Incidence of M on M over g = 101° 24′ = Pr;

of s on s over l = 81° 34′ -- (Pr + ∞)3.

H

=a: b:

Cleavage perfect parallel to Pr+ ∞ (1), less distinct parallel to Pr+ ∞(p). Surface of Pr + ∞ deeply striated in a vertical direction, the other faces smooth.

Refraction double; two axes, the principal one perpendicular to the axis of P, and also to 7. Action of the axis negative. Angle of result ́ant axes about 48° in the plane of P - (g), contiguous to the obtuse lateral angle of P. Index of ordinary Refraction nearly 1.601. Colour grayish-white lustre pearly upon 1, vitreous in other directions. Transparent, translucent.

Hardness 2.5...3.0 Specific gravity = 2.76 of a perfect crystal. Phosphorescence and Electricity, none by heat.

This mineral resembles very strongly Anhydrite and Cryolite, being two species of the order Haloide of Mohs. It is soluble in acids without effervescence. According to an examination by the help of the blowpipe, instituted by Mr. Nordenskiold of Abo, it consists of some of the stronger acids, like the phosphoric or boracic acid, mixed with zinc, some earthy base, and cadmium. Hopeite occurs sparingly in the cavities of several ores of zinc, found at Altenberg, near Aix-la-Chapelle. This interesting substance has been established into a species by Dr. Brewster, who named it in honour of Dr. Hope.

22. Childrenite, a New Mineral.-Mr. Brooke has described the forms of this mineral as being similar to Fig. 3, PLATE VIII. with the following angles :

The forms belong, therefore, to the Prismatic system of Mohs. Cleavage, not observable. Hardness, scratches glass slightly. Colour, wine-yellow. This mineral occurs in small apertures, on the surface of crystallized quartz, found in some part of the ground perforated for the canal near Tavistock, in Devonshire. It has been analyzed by Dr. Wollaston, who found it to be a phosphate of alumina and iron. It has been named Childrenite, in honour of Mr. Children. It resembles sparry iron ore and heavy spar.-See Quarterly Journal, vol. xiii.

23. Somervillite, a New Mineral.-The determination of this species is also due to Mr. Brooke, who named it in compliment to Dr. Somerville, from whom he obtained the specimens. The forms of Somervillite are pyramidal. One of the crystals is shown in PLATE VIII. Fig. 4. The inclination of

P on a is = 147° 5'

P on M = 90

M on e

=

161 33

M on d = 135°
M on M' = 90

Cleavage, perfect perpendicular to the axis, imperfect, if at all, parallel to M or d. Hardness less than that of Idocrase, cross fracture more glassy. Colour, a very pale dull yellow. Occurs at Mount Vesuvius in cavities with crystallized black mica, and another substance not yet examined. According to Mr. Children, it decrepitates by itself before the blowpipe, and melts alone into a grayish globule, with borax, into a colourless one, while Idocrase does not decrepitate, fuses with more difficulty, and yields globules of a greenish tinge.-See Quarterly Journal, v. xvi. p. 274.

24. Nuttalite, a New Mineral.-Mr. Brooke has given indications of this mineral, named by him in compliment to Professor Nuttall of Cambridge, Massachussets. It might be mistaken for Scapolite, with which it agrees in its form, which is a right square prism; but it is softer and more glassy in the fracture; it possesses a play of light, resembling that of some Elaeolite from Norway, and a colour likewise approaching to it.