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part of iron, as an alloy, would be sufficient to account for its magnetical qualities. Dr Wollaston has detected, by chemical means, a small quantity of Iron in Titanium, but not enough to account for its apparent magnetism.

9. Experiments of Mr Barlow and Mr Christie on the Diurnal Variation of the Needle.-Two very able and elaborate papers on this curious subject, by these two active and acute philosophers, have just appeared in the Phil. Trans. for 1823, Part 2d.

From the minuteness of the daily variation, and the extreme difficulty of measuring it excepting with the nicest instruments, its laws, and consequently its cause, are still undiscovered. It occurred to Mr Barlow, that this deviation might be increased, both in the horizontal and in the dipping needle, to between 3 and 4 degrees, by reducing the directive power of the needle, by means of one or two magnets so disposed, as to mask at least, in part, the terrestrial influence. Experiment proved this idea to be correct; and Mr Barlow accordingly instituted a series of experiments. Mr Christie, to whom Mr Barlow communicated his views, also began the inquiry.

Mr Barlow used a delicate and light needle, 8 inches long; and, by means of two magnets, he kept the needle balanced in different directions of the compass, and in these different directions he observed the daily changes in its position. The following were his results for the horizontal needle.

When the N. end of the needle was directed to any point from the S. to NNW., its motion, during the forenoon, is towards the left hand, advancing, therefore, to some point between the NNW. and N. When the N. end is directed towards any point between the N. and SSE., it passes to the right hand, advancing still to some point between the N. and NNW. Hence, there ought to be some direction between these limits, viz. between the N. and NNW., and the S. and SSE., in which the daily motion is zero, or at least a minimum. Mr Barlow likewise concludes, that the daily change is not produced by a general deflection of the directive power of the earth, but by an increase and decrease of attraction of some point between the N. and NNW., or between the S. and SSE.

Having reduced the power of a dipping needle nearly 8 times, by two magnets placed in the line of the dip, Mr Barlow observed, that it passed suddenly from one half-quarter degree to another, more or less, so as to give a difference in the dip of 11° in one day. It seldom, however, shewed any tendency to return, though, when vibrated at night, it commonly took up its morning position, The same sort of daily motion appeared whether the face of the instrument was to the E., W., N., or S. Mr Barlow is of opinion, that the solar light, and not the solar heat, is the principal operative agent in producing the daily variation.

ELECTRICITY.

10. Electricity produced by separation of parts.-In the fine water-proof cloths manufactured by Charles Macintosh, Esq. of Glasgow, where two pieces are cemented together by caoutchouc, dissolved in coal-tar oil, the adhesion is so complete, that when the two are torn from one another in the dark, there is a bright flash of electric light, similar to what is produced by tearing asunder plates of mica, by bursting Prince Rupert's drops, or by breaking barley sugar, or sugar candy. Upon trying this experiment with different substances, we found that flashes of light were distinctly produced, by tearing quickly a piece of cotton cloth.

11. Prof. Cumming's Table of Thermo-Electrics.-In the following table of thermo-electrics, by Professor Cumming, each substance is positive to all below, and negative to all above it, two being used together.

12. New Phenomenon in Electro-Magnetism.-Sir H. Davy found, that when two wires were placed in a basin of mercury, perpendicular to the surface, and in the voltaic circuit of a battery, with large plates, and the pole of a powerful magnet held

either above or below the wires, the mercury immediately began to revolve round the wire as an axis, and with a highly increased velocity when the opposite poles of two magnets were used, one being above, and the other below. Masses of mercury, several inches in diameter, were set in motion, and made to revolve in this manner, whenever the pole of the magnet was held near the perpendicular of the wire; but when the pole was held above the mercury between the two wires, the circular motion ceased; and currents took place in the mercury in opposite directions, one to the right, and the other to the left, of the magnet. Sir Humphry next inverted the form of the experiment. He took two copper-wires of about th of an inch in diameter, the ends of which were flat, and carefully polished, and passed them through two holes 3 inches apart in the bottom of a glass basin, and perpendicular to it. They were cemented into the basin, and made non-conductors by sealing-wax, except at the polished ends. The basin was then filled with mercury to the height of th of an inch above the wires. The moment the contacts were made, the mercury was immediately seen in violent agitation; its surface became elevated into a small cone above each of the wires; -waves flowed in all directions from these cones, and the only point of rest was apparently where they met in the centre of the mercury between the two wires. On holding a powerful magnet some inches above one of the cones, its apex was diminished and its base extended: by lowering the pole farther these effects were increased, and the undulations became feebler; and at a smaller distance, the surface of the mercury became plain, and rotation slowly commenced round the wire. The elevations and depressions in some experiments were th or th of an inch. —See Phil. Trans. 1823, p. 156.

METEOROLOGY.

13. Mean Temperature of London for 1822.-It appears from the Meteorological Journal kept in the Royal Society's apartments, and just published, that the mean temperature of London by Six's thermometer is 55° Fahrenheit, and by observations made at 8 A. M. and 2 r. M. that it is 53°.8, results which appear to be perfectly irreconcilable with one another, unless by supposing either great errors of observation, or great

defects in the instruments employed. As observations made at 8 A. M. give nearly the mean temperature of the day, and as observations made at 2 P. M. give a temperature very much higher than the mean, it is clear that the mean of these must give a result far too great for the mean temperature; that is, 53°.8, upon the supposition of the correctest instruments and the correctest observations, is far above the mean temperature of 1822. This, then, being quite demonstrable, how comes it that the self-registering thermometer of Six, which gives the daily maximum and minimum (the mean observations of which is nearer the mean temperature than 8h and 2h), should give for the mean temperature 55°? This observation merits the particular notice of those immediately interested in the correctness of the Royal Society's observations.-The mean height of the barometer for 1822 was 29°.863, and the quantity of rain 18.068 inches. See Phil. Trans. 1823, Part I.

14. Mean Temperature of the Canaries.-The following are the mean monthly temperatures of St Croix, at Teneriffe, in W. Long. 16° 16′ 48′′, and N. Lat. 28° 28′ 30′′, according to the accurate observations of Don Francisco Escolar.

Jan., 17°.69 Centig. May, 22°.29
February, 17.94

September, 25°.24

June, 23.27

October, 23.70

Do. calculated by Dr Brewster's formula, (86°.3 sin D)-3, 71.13

15. Temperature of the Springs on Ben Nevis.-A young friend communicated to us the following notice in regard to the temperature of the springs of Ben Nevis, and which agree in a general way with those we have made on that celebrated mountain. He examined four of the springs; but as one of them ran near the surface of the ground for a considerable distance before it made its exit, he did not record its temperature. Of the other three, one was about 1200 feet from the base, another about 2000 feet, and the third was the well near the summit. When he left Fort William the thermometer stood in the shade at 56°

(8 A. M.); at the spring 1200 feet from the base, it stood at 48°, and in the spring at 41°.5. At the second spring, elevated about 2000 feet, the temperature of the air was 47°, of the water 38°; and the temperature of the third spring 36°, while that of the surrounding air was 46°.

16. Great Heat at New South Wales.-Dr Winterbottom informs us, that a particular friend, and a very careful observer, saw the thermometer rise, at New South Wales, to 112°, and continue so nearly a week *. The effects of this heat upon the human body were extremely distressing, producing extreme languor, and incapability of exertion. A gentleman remarkably robust and active, out of bravado, to show that he could do what not a man in the colony dared to attempt, took his gun, and went out in pursuit of game; but he was very soon obliged to return, and found some difficulty in doing so. They both described this degree of heat to be so excessive, as to give them a conviction of not being able to support a temperature of only a few degrees higher. The effects of this heat upon animals was such, that the parroquets dropped down dead in the open air. In Africa, where Dr W. resided four years, he once observed the thermometer stand at 103° in the shade, and placed upon the ground (speaking from memory) at 138°. In the Soosoo Country, to the N. of Sierra Leone, at a considerable distance inland, he walked one day about twenty miles, when the thermometer, observed by Dr Afzelius, at present Professor of Botany at Upsal, stood at 991° in the shade; which degree of heat was by no means disagreeable, nor even suspected to be so great by at least 10°, owing to a pleasant breeze which met him. We judge very inaccurately of heat by our feelings, and are more affected by a sudden diminution of 10° of heat than by a much greater increase. The lowest degree of heat Dr W. ever witnessed in Africa was about half an hour before sun-rise, when the mercury stood at 68°, and to the feelings, the cold resembled

2

We strongly suspect some error in this observation. It stood at 96° at Hobart Town on the 3d February 1822, but never rose above 90° during the rest of the year. At Macquarrie Harbour the maximum was 94° on the 1st January 1823; and during Oxley's expedition, the highest seems to have been 81°.