In taking the temperature of the water in the different levels of mines, care was generally observed to select the largest streams, and to put the thermometer at or near the places where they first flow into the mines, so that the influence of any heat from the mines seems to be put out of the question.

It appears that in almost all the mines which have been examined, the highest temperature has been found at the bottom, and it is deserving of notice, that here, in most instances that I have investigated since my last paper, very few workmen are employed; and generally their number increases at each level in ascending from the bottom, as high up as one quarter, or even one-third of the way; so that not very far from the middle of mines, they are frequently the most numerous.

At a level 180 fathoms under the surface in the United Mines, I find the temperature of the water which was, and had been during 12 months, 30 fathoms deep in the mine, was 80°, and a stream of water flowing into the same level, was 87°. This is only half a degree less than it was at the same place in 1820. At that time about 400 men were employed in the mine eight hours each day, and about 50 on an average for the remainder of the 24 hours. When the last observation' was made, only about 200 men worked in the mine eight hours a day, and about 50 during the remaining 16 hours.

I do not dispute, that in close levels, where there is no current, the presence of the men increases the temperature of the air, yet it does not appear by the above table that the heat of the air is usually much greater than that of the water in the same places, perhaps on an average not exceeding 1° or 2°. In many instances, indeed, the water was from 1° to 4° warmer than the surrounding air, and this occurred in several mines at or near the deepest levels.

Before I conclude my enumeration of facts, it may, perhaps, be desirable to state the temperature of the water which flows through the great adit, and is discharged near Nangiles mine, above Carnon Valley. This adit traverses the principal mining district of Cornwall, and extends nearly 30 miles, including its different ramifications, and more than five miles from one extremity to the other in one direction, and three miles in another.

The temperature of the water was taken near the mouth of the adit about six weeks since, and was found to be 69.25°. Richard Thomas, land-surveyor of Falmouth (author of an interesting map of a large portion of our mining district), has ascertained, by frequent observations, that the quantity of water discharged by the adit at different times of the year, has varied from 910 to 1644 cubic feet per minute; but as some deep mines have been set to work since he made his experiments, the average quantity is now probably greater. It appears, on making a comparison of the depth of the water at the time the foregoing temperature was ascertained, with his calculations, that the quantity dis

charged was equal to 1400 cubic feet per minute, or about 60,000 tons per day.

The great adit is divided into three principal branches, the first of which unites with it, at about a mile from its mouth, and communicates with the United and the Consolidated Mines, Huel Squire, Ting Tang, Huel Maid, and South Huel Jewel, the average depth of which mines seems to be about 150 to 160 fathoms. The temperature of the water in this branch near the junction, and about one mile and a half from the mines which principally supply it with water was 73.5°, about the end of last month, when this and the following observations were made. At nearly a mile further on, the great adit is divided into two branches; one of them receives the water from Poldice, Huel Unity, Huel Unity Wood, Huel Damsel, Huel Purk, Rose Lobby, Huel Hope, Huel Gorland, Huel Jewell, and Huel Clinton, the average depth of which is, perhaps, from 110 to 120 fathoms, and the temperature of the water in the branch, at about a mile from the principal mines above named, was 66.5°.

The other branch is connected with Treskerby, Huel Chancer, Chacewater, North Downs, Creegbraws, Huel Boys, Cardrew, and a few smaller mines; their average depth may be estimated at 100 to 110 fathoms, and the temperature of the water in the adit, about three miles and a half from the mines, was 65°.

I have not ascertained the quantity of water discharged by each of these branches; but it is evident they carry off not only the water pumped from the various levels of the respective mines, but also that which is drained from the strata under which they pass, and which is from 30 to 50, and in some places from 60 to 70 fathoms in thickness.

The temperature of the water in the adit is, therefore, even more considerable than might be expected, and the difference observed in the branches may be attributed to the relative depths of the mines with which they are connected, and to many of those communicating with the two last mentioned branches being stopped, or partly full of water.

I have mentioned that the water flows into cisterns at different levels in mines, being partly or entirely retained by the rock on which it rests, but generally from the strata being more or less porous, some of the water sinks through it, and may either mix with an inferior portion, before it flows into the levels, or it sometimes descends in numerous drops, or small streamlets, from the roofs of deeper levels; and in either case, it must produce more or less influence on the temperature, and prevent its being uniform at equal depths.

If there were a perfectly free and open communication between the various portions of water under the surface of the earth, it is evident that mines could not be drained, but the pressure of the columns of water would be irresistible, and their impetuosity overwhelming.

The high temperature in mines seems to have no necessary connexion with the minerals which they contain, since where iron pyrites is very abundant, the heat does not appear to be greater than where it is the reverse.

If, as we may conclude from the evidence adduced from various quarters, that the high temperature which exists under the surface of the earth does not arise from causes merely local or accidental, must we not suppose it either to have been imparted to the globe at its creation, or attribute it to some cause constantly in operation? If the former hypothesis be adopted, it cannot readily be conceived that the heat is conducted towards the circumference of the earth, by the solid substances of which it is composed; for if so, the internal heat must be intensely, and indeed incredibly great; besides, many facts oppose this conclusion; among which it may be proper to notice that granite, and other hard rocks, are generally of rather an inferior temperature compared with clay-slate, and other more porous and softer rocks, which are worse conductors of caloric. It is true we may imagine water and vapour to convey and diffuse heat from the interior of the globe towards the surface, and not necessarily adopt the conclusion, that the heat must be so intense at the centre; but, without setting aside the agency of water and vapour in circulating and equalizing the temperature, may it not with more probability be supposed to depend upon some constantly operating cause? If electricity, for instance, be evolved when several different mineral substances are brought into contact, and likewise in the process of crystallization, &c. may it not, in connexion with the strata and veins, and the almost distinct portions of water which abound in the earth, also act its part on a larger scale, and not only excite heat, but contribute to produce the extraordinary aggregation and position of homogeneous minerals in veins, &c. and the beautiful order which exists even under the surface of the earth? I venture to bring this forward merely as a suggestion, hoping, if it be thought to deserve any attention, that others more competent than myself will investigate the subject.

Note.-I will here mention a fact which I consider to be connected with electricity. Having fastened a piece of iron pyrites with a brass wire in a moss house, the moss being damp, I found on the following day that the wire was broken, and excessively brittle, and the parts which had touched the pyrites were much corroded. On one occasion, after the brass wire had been fastened once or twice round a piece of iron pyrites, and had remained for some days enveloped in damp linen, the constituents of the brass wire were separated, and it was converted into copper wire coated with zinc.

Having recently tried some experiments on the water taken

from the bottom of several deep mines, I find it, in most instances, to contain in solution a very minute quantity of any foreign substance, varying, perhaps, from one to five or six grains in a pint. Its relative purity appears to have no reference to the depth or temperature of the mines; for instance, Huel Abraham, and Dolcoath, are the two deepest, and two of the warmest mines in the county; and the water from the bottom of these mines does not, in either case, hold in solution more than about two grains of foreign matter in a pint. On the other hand, some mines abound with much less pure water. That from the Consolidated Mines leaves 10 grains of residuum from a pint; Huel Unity, 16 grains; from one shaft in Poldice, 19; and from another 92 grains, from the same quantity. In most of the mine-water that I have examined, the muriatic salts, especially the muriates of lime and of iron, are most abundant. I have detected muriate of soda in some instances, particularly in the water from the bottom of the United Mines, the Consolidated Mines, Huel Unity, and Poldice.

Out of the 92 grains of residuum produced from a pint of water from one of the engine shafts of the latter mine, 24 grains proved to be the muriate of soda, 52 grains the muriates of lime and magnesia, chiefly the former, and the remainder muriate of iron, and a small quantity of the sulphate of lime.

The water from another engine shaft of the same mine contained 5 grains of muriate of soda, and about 13 grains of the muriates of lime and magnesia, and the carbonated oxide of iron. All the mines above enumerated are situated in the interior of this part of Cornwall, and are distant several miles from the sea!

ARTICLE VII.

On the Depression of the Barometer in Dec. 1821.
By M. P. Moyle, Esq.

(To the Editor of the Annals of Philosophy.)

SIR, Helston, Nov. 6, 1822. PERCEIVING a wish of Prof. Brandes in the Annals for Oct. that every particular relative to the great depression of the mercury in the barometer in Dec. 1821, might be minutely detailed as it occurred in England, I beg to give my observations beginning with the 24th of the month.

On the 28th, the mercury was at the lowest level with us, though it appears to have been on the 25th on the Continent. The heights taken at 10, 11, aud 1 o'clock, were by measuring the column of mercury from its surface in the reservoir by an accurate rule, and not by the graduated plate affixed to the instrument; but the reservoir is so large that even this great fall made but 0-034 parts of an inch difference in measuring it by the detached scale and the affixed.

I should in the next place state, that my house, or rather the site of the barometer, is 105-30 feet above the level of the sea, for which elevation there ought to be an allowance of 0.104 inch in the height of the column of the mercury. This will reduce the lowest height to 27-516, for 27-620-0-104 = 27.516. This deduction should be made from all the results given by me for the true height.

I am, Sir, your obedient servant,

New Series, VOL. IV.

2 G

M. P. MOYLE.