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up the equilibrium of the air; then, as it is proved by Forchhammer, that more vapour arises from tropical seas than falls there, and that more falls in polar regions than rises in those parts; and as it is proved by the experiments of Volta and others, that whenever evaporation takes place, positive electricity is carried off-it follows that there are electrical currents similar to the currents of air; the vapour, with its electricity, rising in the tropics (thus rendering those parts negatively charged) is carried thence by the superior trade winds to the colder parts of the earth, where the vapour falls; and its electricity escaping to the earth, renders those parts positively charged, whence the electricity rushes off along the earth's surface towards the more negative parts of the earth, and is again carried off by the rising vapour. Mr. Rowell ascribes the direction of the needle, to these currents of electricity from the positive to the negative parts of the earth, and the aurora to the interruption of these currents of electricity, by the dry and non-conducting state of the air in the frigid regions during severe frosts insulating the electricity of the clouds, where it accumulates till it flashes back through the higher and rarer air towards the more temperate regions, thus exhibiting the aurora, and at the same time causing a disturbance of the magnetic needle. The author thinks that many writers have fallen into error in supposing the height of the aurora to be far above the limits of our atmosphere: which error may have arisen from some mistake in their observations, or from some other luminous me. teor being mistaken for the aurora; for as the observations of Parry, Franklin, Richardson, and others distinctly prove that the aurora does take place near the surface of the earth, and is in some way connected with the formation of clouds, the arches which are sometimes seen at such great altitudes may arise from totally different causes. He considers that the diurnal variation of the needle tells in favour of the opinion that the direction of the needle is dependent on evaporation; as very early in the morning, when to the eastward of our meridian, evaporation must be at a minimum, the declination is least: the declination then increases till about the time when the evaporation must be most rapid, and then decreases, till in the evening, it reaches its medium position; and the fact that the diurnal variation is more than double in summer what it is in winter, tells in favour of this view.

The cause of magnetic poles in this hemisphere he ascribes to the quantities of ice blocked up both in winter and summer in the high latitudes above the two continents, thus causing those parts to be the coldest in this hemisphere, and therefore, the magnetic poles; for, as the density of the air from the frigid regions is the cause of the trade winds, and as the density of the air increases with the degree of cold, it follows that more air must flow from the coldest parts of the earth towards the warmer regions than from any other parts, and, consequently, there must be the greatest flow of the superior currents of air from the warmer to those colder parts, thus bringing more vapour and electricity there than to any other parts in this hemisphere. Now if the greatest degree of cold be at the pole of the earth, and evaporation increased regularly thence to the equator, there would then be no declination of the needle, as the electricity would pass off from the coldest or positive parts towards the more negative parts of the earth in the direct lines of longitude; but as the magnetic poles are at a distance from the terrestial pole, and as those parts are more positively charged with electricity than other parts in the same latitude, the electricity must diverge eastward and westward of the direct lines of longitude in passing off to the more negative parts of the earth, and thus cause the declination of the needle.

The author contends that the fact that the aurora did not affect the

needle at Port Bowen, in 73° N. lat., whilst it had great effect at Fort Franklin, in 65° N., tells in favour of his views that the direction of the needle is owing to currents of electricity from the magnetic pole to the more negative parts of the earth, as the American magnetic pole is in 70° N. Mr. Rowell exhibited a large diagram of the earth from the north pole to 40° N. lat., showing at one view the situation of the American magnetic pole according to Sir James Ross, and the Siberian pole according to Hansteen, the lines of equal intensity from Col. Sabine's maps, the lines of equal temperature from Humboldt, the direction of the needle shown by arrows, &c. By the diagram he showed that, in the meridian of the American pole, the lines of equal temperature descend to a much lower latitude than in any part of this hemisphere, which he ascribed to the polar seas there being land locked and causing a great accumulation of ice in those regions, both winter and summer, whilst the magnetic force, also, is the greatest in that meridian.

In the meridian of the Siberian pole, the Polar Sea is far more open, the temperature is higher, and the magnetic intensity less. In the neighbourhood of Behring's Straits, where the Polar Sea is open to the Pacific Ocean, the intensity is still less; but in the meridian of London, or rather to the east of it, the line of equal temperature rises to a much higher latitude than in any other part of this hemisphere, the intensity of magnetism is the least, and the Polar Sea is there open from Greenland to Nova Zembla, and the ice formed in those regions is liable at all times to be broken up and dispersed by the storms of the Atlantic Ocean. He considers the magnetic poles not to be mere points in the earth, but extensive districts in the coldest parts and that even mountains, which from their elevation, are continually conducting electricity from the higher regions of the air, must have some local effect upon the needle. He contends that the opinion is erroneous which ascribes the changes of declination to a rotation of the magnetic poles round the pole of the earth; as we have no proof that the magnetic poles in this hemisphere were ever situated otherwise than in the high latitudes above the two continents; and that the change of declination may be fairly explained on the supposition that the American pole has increased in strength, or the Siberian pole has decreased in strength, and that the line of no variation where the influence of the two poles are equal, has receded during the last two centuries from some point west of England to its present position eastward of St. Petersburgh, thus bringing parts which formerly had an eastward variation to be under the influence of the American pole. He suggests that any geological change which has made the Siberian Polar Sea more open would tend to weaken that magnetic pole; or any change which may have blocked up the American Polar Sea, would increase the strength of that pole. He concludes by again suggesting the experiment of raising electrical conductors, to the height of the clouds in the frigid regions during severe frosts, which he believes would cause the aurora, and also throw some light on terrestial magnetism.

ON THE ATMOSPHERE OF THE MOON, by J. Groby.

WHETHER the Moon has an atmosphere or body of air similar to that which surrounds the Earth, has long been a fertile subject of dispute among philosophers, some affirming its existence, and others as strenuously denying it. Some, who take the negative side of the argument, have urged in defence of their opinion, the constant serenity of the Moon's surface, always undisturbed by clouds or vapours, and even the sallest of the numerous

spots or macula which crowd her surface being at all times equally visible. This certainly would be a very strong argument against an atmosphere were the assertions on which it is fonnded to be relied upon. But this does not appear to be the case; for, on the other hand, there are many astronomers who affirm that the Moon is not always equally clear and distinct, Hevelius says, "that he has several times found, in skies perfectly clear, when even stars of the sixth and seventh magnitudes were conspicuous, yet at the same altitude of the Moon, and the same distance from the Earth, and with one and the same excellent telescope, the Moon and its maculæ do not appear equally lucid, clear, and perspicious at all times." He also adds. "From the circumstances of the observation, it is evident that the reason of this phenomonon is not either in our air, in the telescope, in the moon, or in the spectator's eve, but must be looked for in something existing about the Moon, that is (I presume) in the atmosphere." Again, the existence of a lunar atmosphere has been denied, because the stars, in an occultation, when just about to disappear behind the body of the Moon, retain their full lustre till they seem to touch the very edge, and then vanish in a moment, which phenomenon (it is urged) could not happen if the moon were encompassed with an atmosphere. Here, again, the evidence of different astronomers is at variance, one party affirming and the other denying the fact. Nay, even the same individual has sometimes observed both stars and planets to undergo a change, both in brightness, form, and colour, when close to the Moon's limb, while at other times he has perceived nothing of the kind. A third argument against the existence of an atmosphere (and the last I shall notice) is this. If (it is affirmed) the Moon were surrounded by an atmosphere, then the duration of eclipses and occultations ought to be diminished by means of its refractive power, and hence a celebrated French astronomer (in a memoir written expressly on this subject), has endeavoured to demonstrate that, if such an atmosphere did exist, and its horizontal refraction amounted to only 8", there could never be a total eclipse of the Sun. But (he continues) in the eclipse of that luminary, which happened in 1724, the total darkness continued for two minutes sixteen seconds. Many eminent astronomers concur with the one I have just quoted, in denying that anything like refraction can exist, or has ever been observed to exist about the Moon's atmosphere; others equally eminent assert that they have observed the most unequivocal proofs of it. Both Halley and Euler speak of the evident distortion observable in the Sun's limb in total and annular eclipses. The latter, in particular, says, in the eclipse of the Sun which happened in July, 1748, he observed, that when the uncovered part of the Sun resembled the Moon in her quadrature, the horns of the solar crescent appeared to be bent outwards beyond the circle in which every other part of his disk was comprehended; and when the eclipse became annular, the Sun's disk was dilated beyond the circle which formerly embraced it. This dilation was observed at Frankfort, and was estimated by Euler at 25". Here, then, we have one astronomer observing in a solar eclipse a refraction of 12", while another, from his observations, denies that any perceptible refraction does or can exist. From such contradictory evidence, it seems extremely difficult to draw anything like a satisfactory conclusion. The most probable one seems to be this:-That the Moon is surrounded by an atmosphere in some respects like our own, but much rarer; and that it is differently modified by the peculiar circumstances attached to it. For when we consider that from the slow motion of the Moon on its axis the principal part of its surface is exposed to the direct force of the Sun's rays for fourteen and a-half days and nights, without any intermission, and

NO. 3.-VOL. XVII.

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then, for a like period deprived of them, the one producing a degree of cold beyond anything we can conceive, and the other, a degree of heat sufficient, probably, (if there be water in the Moon), to produce a temporary atmosphere of steam,-have we not every reason to conclude that the atmosphere with which the Moon may be, and probably is, encompassed, is materially different in its constitution and properties, from that which surrounds our own globe, and which may, in some degree, account for the contradictory statements I have just noticed? An annular eclipse of the Sun, presents (I think) the most likely means of obtaining more accurate information on this subject than we at present possess.

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NEW ERA IN STEAM NAVIGATION. In the Washington Union, of January 5th, is a long report from a board of professional engineers and others, appointed by the Secretary of the Treasury, to test an important improvement in the construction of naval steam-engines, the invention of Capt. Ericsson. There appears to be an apparatus called an evaporator, and another a condenser, conveniently arranged amidst the machinery, so as to occupy very little space. By this, the steam, after performing its work, is converted into water, and forced back into the boiler, again and again taking the same routine.

As some of the steam will always be lost by loose joints, the evaporator supplies the deficiency from the element in which the vessel floats, and from this increased supply of steam, the condenser affords any desired amount of fresh water. The whole is said to be complete and perfect, and the following results attained :

1. A steamer may go to sea, and complete her voyage, without ever having one particle of salt water in her boiler, if she will begin it with fresh

water.

2. She need not carry any tanks of fresh water, but can make it from the sea at will; thus saving the space for fuel.

3. Besides the supply for the boiler and culinary purposes, enough fresh water can be made to allow each sailor a bath every day, the supply may be so ample.

4. The fires need never be extinguished to relieve the boilers of salt or mud, as neither salt or mud will ever get in; thus saving fuel.

5. The boiler will require little or no watching; being once arranged, the machinery will do the rest, and keep up the exact supply of pure

water.

6. A boiler at sea, especially in the Gulf of Mexico, will last two or three times as long as at present, as no impurities will be admitted there, any more than on the lakes.

7. Nearly one-fifth of the fuel will be saved, as the heat will act on the plates and flues, free of incrustations from salt or mud, and the water from the condenser, while very hot, will be pumped into the boiler.

8. A low pressure engine will answer on the Mississippi and Missouri, as well as on streams of clear water, as the muddy water will be evaporated, the vapour recondensed, and forced into the boilers as clear as crystal.

9. The awful bursting of boilers, so often occurring on the western waters, may be arrested in toto, as the saving of fuel, and the equal adaption of the low-pressure engine will induce its substitution in lieu of the powder magazines, as the engines now in use may be called.

10. The oil used around the piston of the cylinder, and the rust on the boiler, may impart a little of their taste at first to the steam and water; but a very simple filter will make it as pure as when distilled in the chemist's laboratory.—Hants Paper.

THE DISCOVERY OF COAL AT VANCOUVER'S ISLAND.

The Times having noticed the important discovery of coal in Vancouver's Island, a specimen of which was brought home by the Cormorant, which she had been able to procure at 4s. a ton, while at Valparaiso a ton of British coal was considerably higher; the following interesting particulars, as to the locality of this treasure, are extracted from the same journal:

"On the north and east side of Vancouver's Island, a recently discovered river debouches into Johnstone's Straits, near the mouth of which large seams of coal crop out on the surface of the soil. At the point, the trading steamer of the Hudson's Bay Company navigating the Straits of Juan de Fuca, obtains ready and plentiful supplies, which are put on board by the Indians at a mere nominal price. Mr. Dunn, who was a trader and interpreter in the Hudson's Bay Company's steamer Beaver, gives an interesting account of the discovery of this coal. He states-The cause of the discovery' (of the coal) was as curious as the discovery itself was important. Some of the natives at Fort M'Loughlin having, on coming to the fort to traffic, observed coal burning in the furnace of the blacksmiths, in their natural spirit of curiosity made several inquiries about it; they were told that it was the best kind of fuel, and that it was brought over the great salt lake six months' journey. They looked surprised, and in spite of their habitual gravity laughed, and capered about. The servants of the fort were surprised at their unusual antics, and inquired the cause. The Indians explained, saying that they had changed in a great measure their opinion of the white men, whom they thought endowed by the Great Spirit with the power of effecting great and useful objects, as it was evident they were not then influenced by his wisdom in bringing fuel such a vast distance, and at so much cost. They then pointed out where it could be found, of the richest quality, close to the surface, rising in hillocks, and requiring very little labour to dig it out. This intelligence having been reported at Fort Vancouver, we received instructions to make the necessary inquiries and exploration. Mr. Finlaison and part of the crew went on shore, and after some inquiries, and a small distribution of rewards, found from the natives that the original account-given at Fort M'Loughlin-was true. The coal turned out to be of excellent quality, running in extensive fields, and even in clumpy mounds, and most easily worked, all along that part of the country. The natives were anxious that we should employ them to work the coal. To this we consented, and agreed to give them a certain sum for each large box. The natives being so numerous and labour so cheap, for us to attempt to work the coal would have been madness.' It is earnestly to be hoped that this rich and valuable deposit may ere long be brought within the reach of the fast increasing number of our steamers on the west coast of America and the Pacific."

ASTRONOMY.-Colour of the Stars.-Some undefined circumstances in the constitution of the celestial bodies produces the effect of their exhibiting not only a different degree, but a different kind, of lustre. Their light is by no means uniform; the ray of Sirius differs not merely in intensity, but in kind, from that of Vega: that is perceptible in this country, but in those favoured regions where the atmosphere is more pure, where less of humidity and haze exist, the difference is striking, even to the naked eye; "one star differing from another in glory." One star shines as an emerald, while another glows

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