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the magnetic minerals which it contains, and which should be considered as so many voltaic piles. The elevation of temperature which takes place in the conductors of electric currents, ought also to take place in those of the terrestrial globe. Is not this the cause of that internal heat in the earth, which has been established by recent observations? And when we consider that this elevation of temperature produces, when the current is sufficiently energetic, a permanent incandescence, accompanied with the most brilliant light, without combustion or loss of substance, may we not conclude that opaque globes are so, on account of the little energy of the electrical currents which are established in them, while those that shine by themselves, derive their light from the more active currents which they possess?"

15. Mr Lecount's Method of finding the Dip of the Needle.— In order to measure the dip at sea, Mr Lecount mounts a bar of iron free of magnetism, and about 2 feet long, and upon a stand furnished with a divided quadrant and spirit-level, all the parts of which are either of brass or copper. The stand is then to be placed north and south, and upon a horizontal plane, as ascertained by the level; and, by means of a delicate compass, the bar is examined in different positions, till one side of it is found to be all one pole, and the other side all a contrary pole, and the ends neutral. The divisions on the arc will then give the dip of the needle.-Lecount's Description of the Changeable Magnetic properties possessed by all Iron bodies, &c. p. 53. Lond, 1820.

16. Account of two large Loadstones. In a paper giving an account of three large loadstones brought from Moscow, read before the Wernerian Society on 10th March last, Mr John Deuchar gives the following notice regarding two of them: "The largest loadstone weighs 125 pounds; and it measures in length 10 inches, in breadth 81, and in height 9 inches. When I received it, it could carry 163 pounds; but, by gradually increasing the weight, I afterwards brought it to support 165 pounds, exclusive of a connecting iron of about 28 pounds, and several supports, which might be 12 pounds more; thus giving an improved power equal to 42 pounds. The weight of the second loadstone had not been taken previous to fitting on the armature, but it is

*

This loadstone is now in the possession of Dr Hope.-ED.

supposed to be nearly half that of the large one: it measures in length 51 inches, in breadth 4, and in height about 8 inches. On the 27th November 1818, I had suspended from it a mass weighing 80 pounds, independent of the conducting iron. These two natural magnets were brought to this country in the same vessel: the corresponding poles of both had most probably been placed together, for when they arrived in Edinburgh, the weaker loadstone had its poles changed. A curious fact, which I found exhibited by the largest of these two, deserves particular notice. The full energy of the

south pole was not displayed at E, nor did it

run along the line EF as is usual, but it was

South

F

A

D G

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inch from the

H

south pole, and the force of south attraction ran along the line CD. The north pole, however, was quite correct, being most powerful at H, and along the line HG. This appearance may arise from one of three circumstances: 1st, A be a mass of may ironstone which is not magnetic: 2dly, It may be an ironstone paste, added to complete the shape of the loadstone; or, 3dly, it may be a distinct magnet. If either of the two first suppositions be true, then the power of the loadstone may not be injured by the presence of A; but if the last be correct, then the power must be much weakened. From the external appearance of the loadstone, on both sides of the line of extreme south attraction, I am rather inclined to think that this last is the most likely of the three. If we allow this to be the case, then, by removing A, we must greatly add to the quantity of magnetic effect displayed at the two poles."

ELECTRICITY.

17. Excitement of Muscular Fibre by Voltaic Electricity.The following observations on the subject have been communi

cated to us by Mr John Murray. "In the Journal of Science, No. xix. p. 193, and 194, are detailed some experiments of Configliachi on the excitement of the muscular fibre by voltaic electricity, as modified by the action of poison. In my experiments on the excitability of muscular action by galvanic agency, as modified or suspended by vegetable poisons, detailed in a paper read before the Linnæan Society in 1815, similar phænomena are described. This paper is now more interesting than it may have been at the period referred to. For instance, tinc

ture of opium applied to the sciatic nerves suspended the excitement, but when acetic or other vegetable acid was superadded, the susceptibility was restored. Since, then, discovery has announced an alkali (morphia) as the active principle in opium, a stranger which this phænomenon might have prepared us to expect. There were numerous experiments of a similar description mentioned, as those with Atropa belladonna, Hyoscyamus niger, &c. I subsequently made many experiments on a portion of the Wild Bushman's Poison, brought from South Africa, and transmitted to me by Mr Campbell. The result of my researches was the discovery of an antidote to that formidable poiThis counter poison was caustic potassa. In one of my experiments, a swallow wounded in the thigh by an arrow dipt in the poison was set at liberty, after thirty hours confinement; the arrow being extracted, and the wound washed carefully with the alkali. This was repeated on other animals with equal success. In other cases, this poison, sufficiently rapid in its fatality, was accelerated fearfully by some applications, particularly solution of chlorine."

son.

18. Experiments on the Electric Spark.-It appears from a statement sent to us by our correspondent Mr John Murray, that the electrical experiment of M. Moll, described in our last Number, vol. iv. p. 200. is only a modification of one published by him in the Phil. Mag. for 1815 or 1816, to which the reader is referred.

HYDRODYNAMICS.

19. Compressibility of Water.-In examining Mr Perkins' experiments on the compressibility of water, Dr Roget has found, that he has committed a mistake in the calculation, by which he

makes the compression about 1 per cent. It is actually only

1

212.36

or a little less than one-half per cent. This result agrees most singularly with Canton's experiments, as Dr Roget has shewn; for the modulus of elasticity of water, according to Dr Thomas Young's method, is 750,000, as deduced from Canton's results, while it is 743,260, as deduced from Perkins' results.-See Ann. of Phil. Feb. 1821, p. 135.

20. Perkins' Method of keeping off the Back-Water from Mills. At the time of floods, the Back-Water, as it is called, returns upon the water-wheel, and not only diminishes the height of the fall or head of water, but impedes the motion of the wheel, which is necessarily immersed to a certain depth in the backwater. In order to remedy this, Mr Perkins boards up the wheel against the back-water; but leaves a channel at the bottom, through which the back-water would rush upon the wheel, if it were not prevented and driven back by a superior force. This force is obtained, by taking off from the mill-lead a part of the superabundant water, and allowing it to rush by a new channel, through the channel left in the boarding. Its superior momentum drives away the back-water from the wheel, and allows it to perform its functions as freely and uninterruptedly as if there were no flood in the river. This contrivance has been adopted in the United States with complete success for several years. See the London Journal of Arts and Sciences, vol. ii. p. 38.

METROROLOGY.

21. Meteorological Table, and Temperature of Springs at Leith for 1820.-The following meteorological table has been drawn up by Andrew Waddell, Esq. F. R. S. E. from his own observations at Hermitage Hill, near Leith. The mean temperature of 1820 is 47°, and that deduced from springs 47°.3, —agreeing in a very singular manner with the accurate observations of Mr Jardine on the Crawley and Black Springs, which give for the mean temperature of springs at Edinburgh 47°.08, at an altitude of 230 feet. Mr Waddell's observations were made with a register thermometer, situated within three feet of the ground, and placed in the middle of his garden, the surface of

which is 60 feet above the medium level of the sea; Lat. 55°.58 N.

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January, 34.3 26.3 30.3 8.0 50 4 27

February, 44.5 34 39.2 10.5 54

Mean Temp. of
Spring-water
from a Pump-

well, taken
once in Eight
Days.

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55.1 16.2 82
82 41

64 53

58.5 11.0 73

73 47

56.8 13.7 72 39

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39

October, 50.7 38.5 44.6 12.2 61

32

November, 47.3 37.7 42.5 9,6 56

32

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12.5 65.1 31.8 49.5

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60

39.5

43°.7

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60

49

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50.5

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47.3

22. Mean Temperature at Carlsruhe for 20 years, &c.—The following results of nearly twenty years' observations have been obtained from the meteorological register kept at Carlsruhe by Professor Böckmann :

MEAN TEMPERATURE from 1800 to 1819.

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Jan. Feb. Mar. April, May, June, July, Aug. Sept. Oct. Nov. Dec. 32°.2 36°.5 41°.4 50°.4 60°.6 63°.3 66°.4 66°.4 57°.4 50°.4 41°.4 35°.6

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