and that he attributes it to the same cause that I do, viz. a portion of fixed magnetism in the steel of the balance or its spring. For my part, I think it will not be found possible to ascertain any ship-rate for chronometers which shall correct the errors arising from this cause, from the direction and strength of the attraction of the iron in a ship undergoing such considerable changes as it does in different dips. I always considered the remedy to lie alone in the hands of the maker, who should carefully ascertain that no steel whatever in a chronometer possesses any fixed magnetic quality; and I pointed this out to a chronometer-maker in London in November 1820, shewing him, amongst a number of balances, those which had any portion of fixed magnetism, and those which had not, &c.; but it is requisite, that, in this respect, not only the balance and its spring should be attended to, but that all the steel in the instrument should be deprived of this quality, particularly the steel-spindles of the fusee, barrel, &c. for it is to magnetic attraction, residing wholly in the machine, that I attribute the alteration which takes place in the rates of chronometers on shore in different parts of the world, and which is often very considerable. These attractions may act in several ways. If there is fixed magnetism in the balance, and variable magnetism in the spindles of the wheels, the rate may be altered by any considerable alteration in the dip, as the direction and strength of the variable magnetism will thereby become changed; the same effect may be produced if the fixed magnetism is in the spindles of the wheels, &c. and the variable magnetism in the steel of the balance.

The balance-spring will likewise be acted on under similar circumstances; I should therefore think it absolutely necessary, that all the steel in the machine should be divested of the fixed magnetic quality; the variable ones will have no effect on each other: this can always be done by the action of fire, and if the mechanic, in the process of hardening and tempering the steel, always carefully cools it in a direction at right angles with the dipping-needle, it will rarely be found to possess any portion of fixed magnetism, as, on the contrary, it will be found, that small steel bodies, if heated redhot, and cooled in the direction of the dipping-needle, will often require this quality.

I am of opinion, that this fixed magnetism, if carefully excluded from the machine at first, will not be found to return from the continued motion of its parts.

A very necessary precaution with respect to the use of these instruments, is always to hang them up on board ship at a considerable distance from the compasses. I have known an excellent chronometer rendered useless for the time, by being kept within two feet of the cabin compass, and which, when removed to a different part of the cabin, performed remarkably well.

New Chemical Combination.-M. Dobereiner, professor of Chemistry in the University of Jena, by a series of entirely new experiments, has ascertained that platina, the heaviest of all elementary substances, when reduced into very fine particles, produces by simple contact with hydrogen gas, (the lightest of elementary substances), an electrical or dynamic combination, which, if brought into contact with hydrogen gas or with atmos

pheric air, instantly dissolves itself yielding fire and water. To prove this important fact by a brilliant experiment, M. Dobereiner makes hydrogen pass from a reservoir, by a capillary tube, curved below, upon pure platina in powder, which is contained in a glass tunnel, hermetically sealed at the point, so that the gas mingles with the atmospheric air before it touches the platina. The moment that the current of gas reaches the surface of the platina, the power of that metal becomes red and burning, and this phenomenon continues as long as the stream of gas is directed upon it.

New compound of Iodine. Iodide of Carbon ?-Messrs. Ferrari and Frisiani, whilst preparing the iodate and hydriodate of potassa, observed the production of a new compound of iodine. It may be obtained thus:-Heat an ounce of iodine, with a little water, on a sand bath, and add to it, by degrees, about two ounces of potash; when the two salts above mentioned will be formed. In order to saturate the excess of alkali, pour in, by degrees, a tincture composed of one ounce of iodine to six ounces of alcohol, specific gravity 837. When the re-action of the tincture on the potash is finished, pour the hot liquor on a filter, and the liquid which passes through will, as it cools, deposit yellow crystals, of the substance; they should be carefully washed in cold water, to remove all the iodate and hydriodate of potash.

Another method is, to take the alcoholic solution of the two salts, prepared as above, and distil it and when the fluid which comes over ceases to be coloured, to change the receiver; the colourless liquor then obtained, upon cooling, deposits very pure

crystals, of the substance in question. If the distillation be suspended from time to time, and the retort allowed to cool, beautiful crystals of the substance form in it. If strong alcohol be used in the above operations, and but little water, then, upon adding water to the filtered liquor, the substance is precipitated in abundance. This substance is solid, of a lemon yellow colour, tastes like nitric ether, and has an odour like that of saffron. Its form is a compressed hexahedron (esaedro schiacciato). It is insoluble in water, alkalies, or acids, but soluble in alcohol and ether. It fuses and sublimes by a gentle heat, but at a higher temperature becomes discoloured, is decomposed, and evolves vapours of iodine, leaving behind a mere trace of carbon.-Giornale de Fisica.

Vegetation in Atmospheres of different Densities.-The following experiments have been made by professor Dobereiner of Jena. Two glass vessels were procured, each of the capacity of 320 cubic inches, two portions of barley were sown in portions of the same earth, and moistened in the same degree, and then placed one in each vessel. The air was now exhausted in one, till reduced to the pressure of 14 inches of mercury, and condensed in the other, until the pressure equalled 56 inches. Germination took place in both nearly at the same time, and the leaflets appeared of the same green tint; but at the end of 15 days the following differences existed. The shoots in the rarefied air were six inches in length, and from nine to ten inches in the condensed air. The first were expanded and soft; the last rolled round the stem and solid. The first were wet on their surface, and especially towards the ex

tremities; the last were nearly dry. "I am disposed," says M. Dobereiner," to believe, that the diminution in the size of plants, as they rise into higher regions on mountains depends more on the diminution of pressure than of heat."

Sugar for preserving Fish.Dr. M'Culloch, of Edinburgh, has ascertained that the antiseptic quality of sugar is sufficient to preserve fish in the most excellent condition. He states, that this substance is so active, that fish may be preserved in a dry state, and perfectly fresh, by means of sugar alone, and even with a very small quantity of it. He has thus kept salmon, whitings, and cod, for an indefinite length of time; and by this simple means fresh fish may be kept in that state some days, so as to be as good when boiled as when just caught. It is added, that "if dried and kept free from mouldiness, there seems no limit to their preservation; and they are much better in this way than when salted. The sugar gives no disagreeable

taste. This process is particularly valuable in making what is called kippered salmon: and the fish preserved in this manner are far superior in quality and flavour to those which are salted or smoked. If desired, as much salt may be used as to give the taste that may be required; but this substance does not conduce to their preservation. In the preparation, it is barely necessary to open the fish and to apply the sugar to the muscular part, placing it in an horizontal position for two or three days,` that this substance may penetrate. After this it may be dried; and it is only further necessary to wipe and ventilate it occasionally, to prevent mouldiness. A table spoonful of brown sugar is sufficient in this manner for a salmon of five or six pounds weight; and if salt is desired, a tea-spoonful or more may be added; saltpetre may be used instead, in the same proportion, if it is desired, to make the kipper hard."

On the destruction of Caterpillars on fruit trees.-In May last I (Mr. Sweet, Bristol,) found the gooseberry caterpillar had begun its usual ravages on the leaves of a quarter of gooseberries in my nursery near Bristol. In the last and former season, among many other applications which had been tried, in vain, lime had been used, but in a dry state. I resolved this year to try the effect of it in a different way a bushel of stone lime was therefore slacked, and covered up

for a few hours, to make it more soft and fine; it was then sifted through a mason's sieve of the finest kind, which made it almost an impalpable powder. A man with a light garden-engine was then directed to play water in different directions among the leaves, so that every part of the plants was wet; another man followed closely with a coal-box full of the fine lime-powder, scattering it with his hand, so as to cause it to appear like smoke, and to spread itself on

Gooseberries. The list of cultivated gooseberries includes 47 different sorts of the red gooseberry, 35 of the yellow, 53 of the green, and 44 of the white; of these, the weights of the best specimens are given. The largest red is the Top Sawyer, which weighed 26 dwts. 17 grains; the largest yellow is the Nelson's Waves, 21 dwts. 6 grains; the largest green is the Ocean, 26 dwts. 11 grains; and largest white, the Smiling Beauty, 22 dwts. 18 grains.

Succory as blanched salad.-A variety of this plant, improved by cultivation, is much employed in France. The young leaves are used in salad; and for procuring them, successive growings are kept up in gardens. When the plant is raised in fields, the outer leaves are plucked at different periods of summer and autumn, and given to milch cows, by which it is said they afford about a third more milk than when fed on common fodder, but it at first acquires a slightly sour taste butter is also more easily obtained from it. At the approach of winter, the roots are dug up and laid in a cellar horizontally in alternate layers with sand or light soil, with their heads outtermost and uncovered. In this situation they are kept excluded from frost and also from light, during which they afford the blanched roots called Barbe de Capucin, used as winter salad. The roots are sometimes also put with sand into barrels having numerous holes in their sides, through which the shoots very easily push, and are cut off when required. Barrels thus prepared are sometimes taken on board vessels about to sail, and afford fresh salad for many months.

New Esculent Plant.In the

royal botanic garden of Glasgow, there have been lately received, from the baron de Shack of Trinidad, along with a large collection of rare and valuable plants from that country, several excellent roots of the famous Arracacha. The valuable properties of this interesting vegetable were, we believe, wholly unknown to the inhabitants of the old world, until Mr. Vargas, a native of Santa Fe de Bogota, where this plant is indigenous, brought to England the information, which was published in the first volume of the Annals of Botany, by Konig and Syme. Mr. Vargas states, that the Arracacha is one among the most useful of all the vegetables of that part of America. It belongs to the order of umbelliferæ, and in its habit resembles an Apium (thus bearing some analogy to the celery and parsley of Europe), and it is in some parts of the country called Apio. Its stalk generally divides from the upper part of the root into several stems, thickly beset with large orbicular leaves, gashed into several sinuses, and supported by large tubular leaf-stalks, exceeding a goose-quill in thickness. The roots immediately divide into four or five branches; and each of these, if the soil be light and the weather be favourable, will grow to the size, and nearly the shape, of a large cow's horn. This root yields a food which is prepared in the kitchen in the same manner as potatoes. It is extremely grateful to the palate, more close than mealy

it is so tender that it requires little cooking, and so easy of digestion, that it is the common practice in the country to give it to convalescents and persons with weak stomachs, being thought of a much less flatulent nature than