He next considers what becomes of the vapour, &c., floating from over the tropics toward the poles; which being less affected by the heat of the sun reflected from the surface of the globe, the surrounding electrical fire begins to condense more and more as it moves towards the poles, and the vapours of course to descend; and that part most, which is most remote from, or is the farthest left behind by the sun; and of consequence the higher column of air must tend that way to restore the equilibrium; which motion, at this side the equator, must be to the north-east; and as the vapour, &c., fall again to the earth, the motion must be more to the east. Hence our south-west and westerly winds, which blow a considerable part of the year.

But as this system is too regular to account for the phenomena of the erratic winds, he considers whence they arise. He had before observed, that tracts of land rising into the atmosphere will stop the regular motion of the vapour, &c., and that the vapour being accumulated by succeeding vapour, the subjacent air must be pressed into new directions. Now this cause, added to the daily dilatation of the electrical fire, and the contraction at night, and the coalition of the vapours, to occasion their total descent, will be sufficient to produce a very great variety of winds on this side the tropic.

It now remains to shew, how the general phenomena of the weather and barometer arise from this system. First, why it generally rains in winter, while the wind is south, south-west, and westerly. Secondly, why north-west winds are generally attended by showers in the beginning, and become more dry as they are of longer continuance. Thirdly, why north and north-east winds are generally dry. Fourthly, why the east wind continues dry and dark for a considerable time together. Fifthly, why squalls precede heavy and distinct showers; and why a calm ensues for some little time after they are passed. Sixthly, why storms and high winds seldom happen in a serene sky without clouds. Seventhly, why the vapours in warm seasons, coalesce to form those distinct dense clouds, which produce thunder and heavy showers. Eightly, why the barometer falls lowest in long continued rains attended by winds: and why it rises highest in long continued fair weather; and why the intermediate changes happen. Ninthly, of land breezes, and sea breezes, and water-spouts.

First, the vapours passing the tropics into colder regions, have their surrounding fire condensed by degress; which must increase their specific gravity, and lessen their repulsive power: by which means they must both descend and approach each other, till at last they formed dense visible clouds; and these clouds are also accumulated by other succeeding vapours, of like specific gravity, till they form clouds, which are often several hundred yards in depth, as is often seen in passing through them up the sides of very high mountains. In clouds of such depth, he thinks the coalition of their particles to form drops, may arise from their motion, and the order of specific gravity. Hence he thinks the excess of electrical

fluid will run off among the other particles; by which means the enlarged particles have their specific gravity increased, and are enabled to descend to a lower region of the air. And the more particles they impinge on in their descent, the more their specific gravity and velocity will be increased; and the more their velocity is increased, the more particles will they impinge on, till they fall from the clouds in drops; whose size will be according to the depth and density of the cloud they have passed through.

Having remarked on several of the other particulars above enumerated, in a diffuse and uninteresting manner, Mr. Eeles then adverts to something of land-breezes and sea-breezes, a phenomenon which sometimes happens in fair settled weather, when the wind blows out from the land at night, and in from the sea at day-time. The land-breeze is occasioned by the descent of the clouds, and the particular formation of the land; for if the land rise into a hilly country from the sea, when the clouds and vapours ascend at night, which they often do by the electrical fluid being condensed, they must press the air down the land toward the sea in their fall; as may appear from the smoke of any fire running down the side of a bill, in the evening of a damp day, when the clouds are on the descent. And the sea-breeze is occasioned by the clouds ascending in the day-time, which must impel the incumbent air upwards, and make room for the sea breeze to flow in; but, beside the mere ascent of clouds, there is an exceedingly greater quantity of vapour raised from the land than from the sea. For the same extent of land has an exceedingly greater surface than the same extent of sea; which may appear from the various forms of vegetables and animals, &c., and the greater the surface, the greater will be the evaporation. Beside, the more irregular these surfaces are, the greater will be the reflection and refraction of the sun's beams, which will increase their power. And it is also necessary that the evaporation should be much greater from vegetable and animal fluids, than from fluids in a quiescent state, to carry on a circulation for the great work of nutrition. Now the ascent of these vapours must beget a circulation of the air inward from the sea; in the same manner as the ascent of vapours from any fire brings in the air below to that fire.

As to water-spouts, he says they are oddly described by the learned, as being great columns of water sucked up from the sea by the clouds. But he says, he never saw any such nor could he find, on inquiry from many honest men, who have sailed almost all the known seas, that they ever met any such; and therefore he does not believe that there are any such. There is indeed an appearance something like their description, which may have given rise to their conjectures; but this is no more than a very heavy shower from a very dense cloud, which is drawn into a conical form, and a very narrow compass at bottom, before it arrives at the sea, which it dashes with great violence in its fall.

Dr. Birch, the secretary, by order of the Society, having desired to know the experiments by which Mr. Eeles found all ascending

vapours and exhalations to be electrified; answers, at first he supposed they must be so, according to the reasonings in his letter; but on trial, with a very simple apparatus, he convinced himself they were So. He extended a fine string of silk, eight feet horizontally, and from the middle suspended two pieces of such down as grows on the turf bogs, by two pieces of fine silk, about twelve inches each in length; and then, by rubbing a piece of sealing wax on his waistcoat, he electrified the pieces of down; and then brought sundry burning things under them, so as to let the smoke pass in great plenty through and about them, to try whether the electric fluid would run off with the smoke; but he observed that the down was but a little affected by the passage of the smoke, and still remained electrified. He then brought sundry steams from the spout of a boiling tea-kettle, and otherwise, in the same manner, and still found that the down remained electrified. He then breathed on them in great plenty, but found that the down still remained electrified. He then joined the palms of his hands together, with the fingers extended perpendicularly under the down, which still remained electrified; though the subtle effluvia, thrown off by perspiration, passed in great plenty through the down; as may appear by holding one or both the hands in the same manner under any light matter floating in the air, which will be driven upward, with as great velocity as an electrified feather is by any electrified body held under it.

The electricity remaining in the electrified down after these experiments, made it appear that the smoke and steams must be either electrics, or non-electrics electrified. It was easy to suppose them non-electrics, as they arise from non-electric bodies; and the more, because the highest electrics by a discontinuity and comminution of their parts, long before they come to be as minute as the particles of ascending vapour, become non-electrics, or conductors of electricity. For glass, resin, wax, &c., all become non-electric, even in fusion. But to try whether the steams, &c., were non-electrics, he only bedewed the wax and glass with his breath, steams, &c., from his hand to the end of the wax and glass; and then touching the electrified down with the end of the wax or glass, he found that the electrical fire immediately passed from the down into his hand, through the steams, &c., which rested on the wax and glass. Which he thinks sufficiently proves the steams, &c., to be non-electric; and he thinks it as plainly appears, that they are all electrified while ascending, because the electrical fire in the down does not join with them in their passage through it; which otherwise it would do with them, or any non-electric not electrified.

Steam Electricity.

MR. W. G. ARMSTRONG has again been directing his attention to electricity produced by steam: and seems to have arrived at some very extraordinary results. The boiler employed, was a cylinder

of wrought iron, with rounded ends; its length forty-two inches, and diameter eighteen inches. The iron frame which supported it, also contained the fire; the whole being insulated by resting on pillars of glass. Mr. Armstrong says that, "it is much more convenient and effectual to collect electricity from the boiler than from the steam-cloud; but in order to obtain the highest effect from the boiler, the electricity of the steam must be carried to the earth by means of proper conductors."

Fig. A.

Mr. Armstrong compares the quantity of electricity given out by the boiler, with the quantity produced by "an excellent machine which has a plate of three feet in diameter, which was worked at the rate of seventy revolutions in a minute." The quantity from each source was ascertained by charging a jar to a certain degree of intensity, and allowing it to discharge by a Lane's discharging electrometer: the plate of air between the delivering and receiving ball, being one-third of an inch. The capacity of the jar was nearly half a gallon, and its internal and external coatings together, covered 198 square inches.

The discharges of the jar, by the action of the machine, were twenty-nine per minute; and those by the electric action of the steam boiler, were 220 per minute; which, in favour of the steam apparatus was more than seven to one. Sparks twelve inches long were taken from the boiler, notwithstanding the great dissipation from the metallic edges of the boiler and frame, from the dust and flame of the fire, &c.

Mr. Armstrong thinks that in order to obtain a "high development of electricity," that a slight intermixture of water with the steam is necessary; though in previous experiments, with a gun-metal boiler, this did not appear to be the case. The discharging jet which Mr. Armstrong finds most useful, is of hard wood, such as ebony or partridge wood (See Fig. A): in fact a wooden plug about an inch and a half long, with a cylindrical hole, about one-eighteenth of an inch diameter, throughout its axis. To the inner end of this perforated plug is attached a brass cap, with a steam channel of a peculiar shape; the principal feature of which is a slit made by a saw, in the side of the brass piece, reaching a little farther than, and at right angles to the axis (See Fig. B). A communicating channel between this slit and the wooden opening,

Fig. B.

is formed by a cylindrical opening, one-tenth of an inch in diameter, in the axis of the brass: the axis of both cylindrical openings are thus coincident, or in the same right line. The channel of the brass piece is very conveniently represented by the letter T with one of its arms wanting. The remaining arm would then represent the lateral slit, and the stem of the letter would represent the axial hole, which leads to the wooden tube. Hence the steam first enters the lateral slit, and after leaving the brass traverses the wooden jet tube. We must remark, however, that as this apparatus is fixed into the outer extremity of a stop-cock, the steam necessarily traverses the axis of the stop-cock before it enters the slit.

Mr. Armstrong still insists on the correctness of his former views respecting the mode by which the electricity is excited: viz., by the friction of the steam at the jet. Yet he says, "As the mode of ejection which I have described, is neither characterised by peculiar violence of friction, nor by great extent of rubbing surface, I feel great difficulty in accounting for its extraordinary efficacy, upon the supposition that friction is the exclusive clause of excitation."

In some experiments Mr. Armstrong employs several jets at the same time, screwed into different parts of "an iron vessel, which communicates with the boiler, and in which the proper quantity of moisture to be carried out with the steam is deposited by condensation. The steam is used at a pressure of 70lbs. on the square inch, and discharged horizontally in diverging jets. Each jet affords quite as much electricity as a good electrical machine of ordinary dimensions."

The most important points of information in a series of experiments of this kind, are unfortunately left unnoticed. Mr. Armstrong makes no mention of the influence of the moisture that is mixed with the steam, nor does he say whether the electric action of the boiler, or that of the steam, was of the positive or negative kind. W. S.

On the Aurora Borealis. By JOHN RICHARDSON, M.D., F.R.S., F.L.S., M.W.S., Surgeon and Naturalist to the Arctic Land Expedition.*

THE results of the observations of this phenomenon made during the present expedition, coinciding with the remarks on the same subject, given at much length in the appendix to my former narrative, I shall here confine myself to the mention of a few brief deductions from a careful examination of our registers at Bear Lake. The observations were made without intermission for six successive months in the years 1825-26, and again in 1826-27.

My opinion, recorded in my former narrative, that the different

• From the "Edinburgh New Philosophical Journal," September, 1828.