He has shown that in this interval the produce has increased more than fourfold. This work, very important for the administration, is accompanied by a very interesting chart, exhibiting the extent of our coal districts, the principal mines at present working, and the direction of their different levels. It has been inserted in the Journal des Mines.

A shower of stones has fallen this year likewise in the neighbourhood of Langres, with all the usual circumstances. M. Pistollet, physician in that town, has collected some of them. They are quite similar to other stones of the same origin, except that their fracture is perhaps a little whiter.

M. Vauquelin, who had been charged last year with the examination of the aerolites of Agen, has presented some reflections on the state in which the principal elements occur in this sort of stones. A portion of the silica appears to him to be in combination with the magnesia. Sulphur is present united to iron; for the mineral gives sulphureted hydrogen, when dissolved in the acids. As to the chromium, it appears in a separate state, and sometimes in particles so large as to destroy all idea of combination.

(To be continued.)

ARTICLE XI.

SCIENTIFIC INTELLIGENCE; AND NOTICES OF SUBJECTS
CONNECTED WITH SCIENCE.

I. Flexible Sand-stone.

Some fishermen, upon the east coast of China, near the province of Chincheu, brought up a considerable piece of stone in one of their nets. Observing something peculiar in its appearance, instead of throwing it overboard, they carried it to Canton to tempt the curiosity of the Europeans in that place. It was purchased by Mr. Garratt, the purser of an East Indiaman, who supposed from its appearance that it was a petrified buttock of beef, and on that account gave a considerable sum of money for it. It is at present in the possession of Mr. Mawe, mineral dealer in the Strand, * where I had an opportunity of examining it.

It is an irregular shaped mass, weighing, when dry, 23 pounds four ounces avoirdupois; and when soaked in water, 24 pounds four ounces. It has certainly some faint resemblance in shape to a buttock of beef. One part answering to the bone and another to the flesh. But this appearance is owing to an external coating of ochre, and does not hold internally. On one side of it there is a coating of small quartz crystals. The stone is full of small round holes, placed at unequal distances, and not penetrating deep. Colour partly snow white, partly wine yellow.

manganese has the same property of absorbing various doses of oxygen; but have not yet heard whether it be capable of furnishing it to the roots of plants. Sir H. Davy, I think, says that oxide of iron is very useful in vegetation; but of oxide of manganese he has not said a word. Should you think it worth your while, you will much oblige a constant reader, and numerous others who are engaged in clay-burning, by explaining what you conceive to be the benefit derived from this process. I have seen some fields having had the whole surface ploughed up, being a clay soil, and a good deal of vegetable remains mixed with manure, subjected to this wasteful torrefaction. Manure in Scotland is difficult to be had, and the management of it not at all understood. Surely this method of destroying it in the soil is most wasteful, and will finally prove highly injurious to the interests of agriculture, if not soon checked. If at any time you should find leisure, some papers on the management and preparation of manure on sound chemical principles, introduced into your publication, would be well received by your northern friends. With hopes of soon seeing your attention given to the explanation, and what you conceive may be the advantages of clay-burning,

I remain, dear Sir,

A CONSTANT Reader.

I am sorry that I am quite unable to give a satisfactory explanation of the practice alluded to in the preceding letter. On reading Mr. Craig's letter on the subject, when in Edinburgh last year, I made some inquiry about it, and was informed (I think) by Professor Jameson that he had seen some specimens of the clay thus burnt, and that in reality it was a marl. This explanation satisfied me at the time; but it is quite obvious, if the sub-soil from Port Patrick to Berwick be treated in this manner, that its nature must vary greatly in different places.

The burning of clay as a manure is not a new discovery, as it is supposed to be, in the Farmer's Magazine. Dr. Reid, in a letter to Lord Kames, written in 1775, says, "If wet clay is put into the fire uncompressed, I am informed that it burns to ashes, which make no bad manure." (Life of Lord Kames, vol. iii. p. 224.) We can assign some conjectural advantages that may result from burning clay, and laying it as a manure on clay land. From the curious table by Dr. Schübler, inserted in the last number of the Annals (p. 208), we see how very adhesive (or heavy, as agriculturists term it) clay soil is, and how strongly it retains moisture. Now when clay is burnt it loses these qualities. Such a mixture, therefore, may tend to render a clay soil less adhesive, and less retentive of moisture; but if this be its only use, fine sand or calcareous sand would probably answer better.

From Mr. Craig's description of the burning, we may infer that the heat applied is very small; for he says that the combustion is not apparent, unless you open up the heap; and that in such a case

it goes out, and cannot be again kindled. Is it not, therefore, possible that this apparent burning of the sub-soil is in fact only accomplishing imperfectly what Mr. Vanderstraeten says is performed every third or fourth year in Flanders. In that country, according to him, every third or fourth year the sub-soil, which is soaked with the manure that has been laid on the surface, is brought to the surface by trenching the whole ground, while that which was formerly the surface is converted into sub-soil. By this method he says the necessity of fallowing is saved; for the sub-soil in reality lies fallow for three successive years.

In case our farmers should be tempted to try this experiment, it may be proper to mention that the Waes, or the country between Antwerp and Ghent, in which Flemish farming has been carried to the highest point of perfection, was originally nothing but sea sand, and that it has become the rich, light soil, which we find it at present, from the great quantity of manure laid upon it, for a period of at least three centuries.

SIR,

V. Lamp for Coal-Mines.

(To Dr. Thomson.)

Pereant qui ante nos nostra invenerint aut dixerint.

I again prefix my motto by way of correcting the press of the last month. The figure of the lamp is at once an answer to the objection in The Philosophical Magazine, that the tube may receive explodible air from a blower, whether the lantern be moving or stationary. The safety principle of Sir H. Davy's lantern was at first supposed to be foul air within the lantern derived from the combustion of the wick. This was an error; and the diminished flame has been shown to be owing to the diminished supply of air. At first air was admitted by one or two large holes at the bottom of the lantern; explosions took place; to these holes, diminished in size, and increased in number, tubes were added. Finally, the holes were multiplied until they deviated into gauze. At every progressive change The Philosophical Magazine abused those who doubted. If I am now asked if I trust in the gauze, my reason for doubting is the abuse which The Philosophical Magazine continues to bestow on all who shall doubt. You have not developed the principle upon which the benefits of the gauze depend. You talk of a fixedness of the air, which cannot be. If an explosion takes place, without any considerable extrication of heat, the contact of the adjacent wires cools down the red-hot air, and renders it incapable of kindling combustion without. This indicates an adaptation of apertures and wires, which will vary with the nature of the explodible air and the heat developed. There will be, then, no safety but what depends upon this due arrangement, and the access of explodible mixtures not yielding more heat in combustion than is provided. If this heat be in excess, if a stitch be dropped

in the gauze, if the gauze be burst by the explosion, all is lost. Will a bomb inclosed in metallic gauze explode in a magazine without firing it?

To Sir H. Davy all credit is due for the perseverance with which he has continued to review, and endeavoured to improve, the first suggestions of his mind, and for the benevolent purposes by which his labours have been actuated.

Complete success seems not to be attainable in any of the ways attempted, and security should rather be expected from the change of system which has been before recommended.

VI. Results of Hygrometrical Observations made in the Basin of the Atlantic Ocean.

A gardener's wife at Vienna was, at the age of 24 years, seized by a violent headach, which continued for several years, and drove her almost to despair. She was at last advised to take snuff as á remedy, in order to promote a discharge of mucus. Happening to have some assafoetida in the house, she mixed it with the snuff, on the supposition that it might increase the effect. The consequence was, that a worm was discharged from the nostril similar in appearance to the common grub. This circumstance induced her to continue to use the mixture of assafoetida and snuff. Eight more worms were discharged. In short, by the use of the remedy, 48 worms in all were discharged, and the headach was completely removed. Dr. Frank, who relates the case, supposes that the worms had been lodged in the frontal sinus.

An experiment was lately made at Blackwall to determine the strength of the fron employed in the manufacture of iron cables. It was found that an iron wire 14 inch in diameter was broken by a weight of 40 tons; therefore an iron wire of one inch in diameter

would be broken by a weight of 25'6 tons. This is considerably less than the strength of iron resulting from Sickingen's experiments. He found that an iron wire 0-078 of an inch in diameter was broken by a weight of 549:25 lbs. avoirdupois. Now if we suppose the strength of iron wire to vary as the squares of its diameter, the preceding experiment will give us the weight capable of breaking an iron wire of the diameter 0078 of an inch 348.88 lbs. avoirdupois. Hence, supposing both experiments correct, English iron must be materially weaker than Swedish iron.

IX. New Ore of Copper.

Mr. Mawe, mineral dealer in the Strand, received some time ago a cargo of minerals from Cadiz, which had been shipped originally at Vera Cruz, and of course are the produce of Mexico. Among them there were a few specimens of a copper ore, which, to me at least, was new; nor have I been able to find any allusion to it in any of the mineralogical books which I have consulted. The specimens which I have seen being few and small, the following description will be imperfect:

Colour, verdigris-green, with a tint of blue. The central parts of the distinct concretions appear darker coloured than towards the circumference, owing, I conceive, to the translucency of the edges of these concretions. Some few of the concretions are coated with a whitish crust, but this is uncommon.

Most of the specimens had a botryoidal form; one of them was thin, as if it had constituted a portion of a thin vein.

Lustre, vitreous, and varying much in intensity. The internal lustre of a distinct concretion fully as strong as that of glass; but the external lustre is often dull.

Fracture compact, conchoidal. Fragments somewhat rounded with blunt edges. In granular distinct concretions rather larger each than a grain of mustard seed. Translucent on the edges. Nearly as hard as calcareous spar. It is readily scratched by a knife. The distinct concretions are very easily separated from each other; but a single concretion is not more easily frangible than alum or rock salt. Brittle. Specific gravity 2.238.

When a distinct concretion is thrown into nitric acid, no effervescence takes place; but if we reduce the mineral to powder, it effervesces in that acid, and is partly dissolved. The same solution takes place in the course of a few days if a lump of the mineral be put into nitric acid. A white insoluble powder remains, which fuses into a glass with potash, and is therefore silica. The nitric acid solution is blue, but becomes green when mixed with muriatic acid. 241 grains of the mineral treated in this way furnished 6.1 grains of silica; and the copper, being thrown down by a plate of zinc, weighed 10.5 grains. Now 10.5 grains of copper constitute 13: 125 grains of peroxide of copper. This oxide in the ore was united to carbonic acid and carbonate of copper, as I have ascertained by experiment, and is composed of one atom acid and one atom