may be the direction of the magnetic current to that of the motion of the disc, the phenomenon of rotatory magnetism still appears. On raising the revolving plates to various temperatures, even up to a red heat, still no difference was observed between their action then and at ordinary temperatures. These experiments are difficult of performance, but M. Haldat intends to pursue them in an unexceptionable manner, especially for the purpose of observing what will happen with a steel plate, which at high temperatures will, in coercitive power, be brought to a level with soft iron, and into the same condition with it.-Ann. de Chimie, xxxix. 232. 3. Refraction of light by bodies in different states.—One of the consequences deduced by Newton from his theory of light, is that the refractive powers of bodies of the same kind, but of different densities, is proportional to the density. Exceptions to this law were first shewn by MM. Arago and Petit, who found that the vapours of ether, and carburet of sulphur, had refractive powers, which, compared with those belonging to the same substances in the liquid state, were less than they ought to be when calculated from the comparative density of the fluids and their vapours. More lately, M. de la Rive has examined the same point in the theory of light, by reference to experiments on the condensible gases. Liquid sulphurous acid, for instance, he finds to have a refractive power a little greater than that of water, whereas, calculating from the refractive power of the same substance as a gas, ascertained by M. Dulong, it ought to have, in the liquid state, a power only of 0.661; but water has a power =0.784, and, by experiment, sulphurous acid is still greater, hence another instance in addition to those mentioned above. Calculating in a similar way, and from the experiments of M. Dulong upon the gases, what ought to be the refractive power of liquid ammonia and liquid sulphuretted hydrogen, they come out as 0.752 and 0.767, both of which are less than 0.784 or the power of water, although, according to Mr. Faraday's experiments, both these condensed gases have a greater refractive power than water.-Bib. Univ. xl. 207. It may be doubted, from the difficulty attending the only method in which Mr. Faraday could take the specific gravities of ammonia and sulphuretted hydrogen, whether the results are sufficiently accurate for conclusions like those above. The densities are given merely as approximations; and it is evident the bulbs he used must have been altered by the pressures to which they were subjected.-Ed. 4. Horizontal Force of a Magnetic Needle.-It has been announced to the Academy of Sciences by M. Dulong, that M. Babinet has determined the horizontal magnetic force of the earth by a method derived from that invented by Poisson in 1825, but by experimental processes and calculations different from his. He has not resorted to the oscillations of a magnetic needle, but obtained the magnetic force by the torsion of metallic wires, and by the isochronous vibrations of copper needles of a given weight. The force of the earth is almost entirely compensated for reciprocal actions, by the direct torsion of a properly selected wire, which is fixed below the lever carrying the moveable needle. Ultimately, M. Babinet arrived at the following theorem:-A magnetic pole, which, at the distance of a metre (39.37079 inches), acts on an equal pole with the force of one milligramme (0.0154 grains), is directed by the earth with a horizontal force 320 times as great (i. e. 4.928 grains.)—Revue Encyc. xli. 827. 5. On the flowing of Sand under Pressure.-A year or two since, M. Huber Burnand described an anemometer to the Philosophical Society of Geneva, in which the force and duration of the wind were ascertained by the quantity of sand which escaped from an aperture varying in its size with the wind. In consequence of conversation relative to the manner in which sand would flow, and how far it would accord with liquids in this respect, M. Huber undertook a set of experiments which have given some very curious and interesting results: these we shall endeavour very briefly to abstract. To obtain a regular fall of sand, it must be well sifted, but must not be too fine. That which will just pass through a sieve containing 38 wires per inch in one direction, and 45.6 in the other, flows with great facility; but the aperture must never be less than .079 of an inch in diameter. The sand, in the experiments, was generally contained in wooden boxes, closed at the bottom by four moveable plates, so that the aperture could be widened or lengthened at pleasure, the edges of these plates being bevilled on the exterior. The sand which had passed the aperture was estimated both by weight and measure. The quantity of sand which flows in a given time through a given aperture is the same, whatever be the volume, the weight, or the height, of the sand in the box above. The height was sometimes increased tenfold without change. When the aperture was from .078 to .118 of an inch in width, the quantity of sand which passed was always directly as the length of the aperture; but the least increase in the width occasioned an increased quantity greater than in the direct ratio of the areas of the apertures. The first part of this result may be useful in the construction of numerous instruments. Sand passing out by lateral apertures made in the surface of the boxes flowed with equal velocity, whatever the height of the columu within; but if these lateral apertures were made in the form of horizontal holes, and the diameters were not nearly equal to the length, not a grain of sand would pass. Sand being poured into one leg of an inverted syphon did not mount in the other. It extended but a very little way into the hori zontal part. Whatever pressure be given to the upper surface of the sand, it exerts no influence on the issue below. From a quarter to half a hundred weight produced no difference. A rod placed upright in the sand, directly over the aperture, descended without any inclination, in a very regular and uniform manner. When placed between the centre of movement and the border of the box, it also moved regularly, but gradually became inclined. M. Huber remarks that there is perhaps no other natural force on the earth which produces by itself a perfectly uniform movement, and which is not altered either by gravitation or friction, or the resistance of the air: for the height has no influence; friction, in place of being an obstacle, is the regulating cause; and the resistance of the air, within the column, must be so feeble as to be alto gether insensible as a disturbing force. Single grains of sand placed upon a flat surface did not roll until the inclination of the surface was at least 30°, sometimes almost 40°. The angle formed by a heap of flowing sand is almost always between 30° and 33°; very rarely as much as 35°. Small shot and pease produced the same general effect as those described with sand. An egg was put at the bottom of a box, and covered a few inches deep in sand: a weight of 60 lb. or more placed over it did not injure or affect the egg. The same result took place when the sand at the bottom of the box was put in motion by opening the aperture. Hence it is evident that the sides of the vessel support the pressure almost entirely; and also that the egg is protected from the irregular action of the pressure by the sand, to the same degree, though not in the same manner, as if in a liquid. Other experiments fully proved that the pressure of the sand was principally sustained by the sides of the vessel. An inverted syphon had a little mercury poured in until both limbs were partly filled, and then sand was poured in on the one side upon the mercury: no elevation of the mercury in the other leg took place. Pressure was added to the weight of sand, still the mercury remained unmoved. More delicate experiments, by means of balances, showed the same effect. A simple paper tube was rolled up; a plug fitting very loosely into the end, but not so that sand could pass it, was floated by a cork or otherwise, on water, with such buoyancy as to be able to sustain the little cone of sand that its circular surface could receive, and then the tube was held in the hand over it. On pouring sand in, the tube might be filled without displacing the floating plug below, although there was weight enough to sink plug and tube, and every thing else, if the hand had been taken away. The sides of the tube, in fact, supported the sand. From these, and other experiments, it was concluded that it would be exceedingly difficult to push sand out of a tube; and upon trial, this was found impossible; the sides of the tube gave way first. APRIL-JUNE, 1829. 2 D Even when inclined 20° downwards it could not be done. It is easy, therefore, to see how, in the blasting of rocks, sand is as effectual for closing the hole as a plug, the most compact driving, or any thing else. A very simple mode of shewing the most striking of these effects is to prepare an open tin tube, an inch in diameter, and of any length; to press a piece of thin paper against the end of it with the hand; to moisten the edges of the paper; and, replacing it, to let it adhere simply by such moisture; then placing the tube upright, with that end upon the table, to fill it with sand, and afterwards gradually to raise it. Whatever the weight of the tube and its contents, it may be carried any where in that position, although the paper bottom adheres but very slightly.-Bib. Univ. xl. 22. 6. Improved Method of fixing the Mariner's Compass.-This im provement is due to Mr. Lemuel Langley, of Norfolk, in the State of Virginia. It is the object of a patent, and is thus described :"The object of my improvement is to dispense altogether with the binacle in which the compass is ordinarily fixed; to cause it to answer all the purposes of a tell-tale, and to secure it against accidents from cannon shot, the shipping of heavy seas, or any other cause of injury. The mode in which these ends are attained is by cutting a hole through the deck of the vessel, at or near the place where the binacle is usually situated. This hole is cut through into the cabin, and within it is placed the compass, with its box, suspended in the usual way; and when so situated, it is completely out of the reach of cannon or other shot. In order to cause it to act as a tell-tale, the compass box is made with a glass bottom, so that the card can be seen as perfectly in the cabin as upon deck. I also make the compass card translucent, or semi-transparent, in consequence of which it may always be lighted from below, and will be much more plainly seen at night than when lighted in the ordinary way. The compass is defended at the top by a very thick piece of glass such as I have used has been three-fourths of an inch in thickness; and this is also defended by a rim or band projecting above the deck. The lower side of the box is also glazed; and I contemplate sometimes making the sides of the box of glass, should it be desirable to admit light that way." The editor of the Franklin Journal speaks strongly in praise of these compasses. 7. Smoke Disperser of M. Millet.-A report upon this apparatus, made by M. Derosne, speaks favourably of its powers. The apparatus is simple, consisting of a kind of tub pierced with a great number of holes, having the burs outwards. It has been taken into practice by many persons. In order to prove its efficacy, one of them was fixed on the top of the funnel pipe of a stove, and a very close, smoky fire made below. By means of a ventilator, an artificial wind was then made to strike directly and powerfully on the smoke disperser for the purpose of driving the current downwards and making the stove smoke; but neither by this, nor even additional means, could any effect of the kind be produced. The committee could not explain the effect, except by supposing that the cylindrical form of the apparatus presenting only a small surface to the action of the wind was favourable, and that the form of the small apertures in this cylinder, occasioning a great number of contrary currents, produced almost a perfect neutralization of the force of the wind. Whatever may be the cause, the apparatus offers a cheap and effectual remedy for smoky chimneys, when this fault in them is dependent upon the pressure exerted by winds upon the upper aperture of the flue.-Bull. Soc. Enc. 8. Enamelled Street Names.-Recently the names of the streets in Paris have been put up on enamelled plates, the ground being blue and the letters white. The substance on which the enamelling is performed is lava in slabs, and its use was suggested by the Count de Chabrol. The prepared tables have been submitted to Brard's test, and also to great differences of temperature, without suffering injury. The same substance (lava) has since been used as the basis of certain enamelled designs; it is much superior in some points to porcelain in this application, because the necessary exposure to fire does not cause it to crack in the manner that porcelain does, and which often, with the latter substance, is followed by the destruction of the artist's work.-Jour. de Paris. 9. Examination of Patent Claims.-Since 1826, the applications for patents in Piedmont and Sardinia have been referred to the Academy of Sciences at Turin, with the intention of negativing all those founded in ignorance or knavery, and supporting only those which are true improvements, and in their effects really advantageous to the arts. Although the number of patents has been excessively diminished in consequence, yet it appears that the applications have increased in an extraordinary degree. The academicians, though much engaged in the year 1826 in examining claims, were poorly rewarded by the occurrence of actual improvement: only two machines were 'brought forward which received their sanction. 10. Detection of Potatoe Starch in Wheat Flour.-M. Chevalier says, that when flour, adulterated with potatoe starch, is sprinkled upon black paper, and examined by a powerful lens, or a microscope, the starch may be detected by the brilliancy of its grains. 11. On Adulteration of Wheat Flour, by M. Henri.-Many varieties of flour have been submitted to us to ascertain the presence of potatoe starch in them. By the aid of a good lens it was easy to see certain brilliant and crystalline points in them; but not being in this way able to ascertain the proportion mixed with the wheat, we thought it would be better to determine the quantity of gluten in them, and |