He then considers the possibility of their being streams of fluid somewhat denser than water, and flowing around the planet. The extraordinary thinness of the ring allowing the fluid to be supposed to be of uniform density; then with the mass, width, diameter, and velocity of rotation as observed, a proportion for the thickness and width of each ring, may be computed by the respective lengths in each direction, which will give equality of fluid pressure in the centre. Hence the whole number of component rings to make up the grand ring as observed, may be computed, and the first approximation has given 20, which Prof. Pierce considers the maximum limit. The definite width of the elementary rings, is, he says, to a certain extent, analogous to the definite size of the drops of water from a vial; and as those drops may be observed to break off from the fluid above with quite an abrupt line of separation, so will the dividing of the rings of Saturn, as the fluid approaches that state of rest which is necessary for the phenomenon, occur with a swift and abrupt sinking in at the proper distances.

Investigating then into the stability of such a fluid ring or rings, Prof. Pierce was surprised to find that after all, the motion of the centre of gravity was not controlled by the primary; that it retains the individual particles from flying apart, and keeps them in the form of a ring, but it has no influence on their motion as one body. The ring might therefore, so far, move to such an extent in its plane as to be brought into contact with the ball of the planet and destroyed. He found, however, that the sustaining power exists in the satellites exterior to the ring, as was indeed supposed by Sir John Herschel, in his Outlines of Astronomy.

Thence Prof. Pierce concludes, that no planet can have a ring, unless it is surrounded with a sufficient number of satellites properly arranged; and that Saturn is the only one so furnished. He shews moreover, that the Sun has not its satellites, i.e. the planets, properly arranged for supporting a ring, or that the only possible part of the system for such a phenomenon would be just within the powerful masses of Jupiter and Saturn, and that supposing the Sun ever had been surrounded by some ring of matter comparable to the zodiacal light, then defects in the maintaining power of the planets outside might cause the centre of gravity of the ring to begin to move until is was broken by being brought into contact with the Sun or some of the interior planets, when either asteroidal planets or comets might result under different circumstances.

Pressure of business has prevented Prof. Pierce at present from giving the whole of his mathematical investigations, but meanwhile his results will be received with great faith, after the unusual ability and the scrupulous regard to absolute truth of hypotheses which he shewed in his difficult researches into the mutual perturbations of Uranus and Neptune.

New Planet Eunomia.-As Messier complained that when grieving

for his lost wife, some other astronomer had succeeded in finding a comet, which would otherwise assuredly have fallen an earlier prize to his superior skill in searching the heavens; or as Bonaparte exclaimed on hearing of the battle of Trafalgar when he was on the victorious field of Austerlitz, that "he could not be everywhere at once;" so the great English planet discoverer, Mr Hind, may complain that he cannot be attending to everything; that when he goes with a portable instrument to observe a total solar eclipse in a foreign country, he cannot be searching for new planets in Mr Bishop's Observatory. And at least it is an additional proof of the richness of the field of discovery, that when almost all the astronomers of note had gone to the Continent to observe the eclipse of July 28, another, M. Gasparis, of Naples, who could not stir from home, succeeded in finding, only the next day, another of the asteroidal planets. It appeared as a star of the 9th magnitude, and has been named Eunomia. Its place amongst the other members of that celestial family, will be found by the following determinations, viz., mean distance = 2.46, periodic time 1406 days. Its position in the sky, when found, was 18h 16m, R. A., and 26° 4' south declination.

New Satellites of Uranus.-On November 3d, Mr Lassel of Liverpool, as active and successful a discoverer of satellites as Mr Hind or M. Gasparis of planets, wrote to announce of his suspected discovery in October 24th having been confirmed; and that he can now state confidently, that Uranus has two satellites interior to the closest, suspected by Sir W. Herschel. This had a period of five days, but the two new ones have for their time of revolution four days, and 2.5 days respectively.

"These new satellites," he 66 says, are very faint objects, probably much less than half the brightness of the conspicuous ones, and generally the nearest has appeared the brightest. All four were steadily seen at one view in the 20-feet equatorial, with a magnifying power of 778 in the more tranquil movements of the atmosphere. The finest definition of the planet and freedom from all loose light in the field of view is necessary for the scrutiny of these most minute and delicate objects."

Standard Thermometers.-Mr Sheepshanks, who has been engaged for some time past in the construction of a standard scale of length, has at last got over one of the principal difficulties, viz., procuring sufficiently accurate thermometers to ascertain the temperature, and the consequent expansion of the scale. His success here will doubtless be of service to others elsewhere, as a thermometer is so essential an instrument of all scientific research, and though so apparently simple, is one of the most difficult problems in practical science. The stage of accuracy to which Mr Sheepshanks has arrived, is to be able to depend on a thirtieth, or even a fiftieth, of a degree of Fahrenheit; the height of the mercurial column being read off by a small telescope and micrometer. The bulbs are gene

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rally about to inch in diameter, and the tubes, which have the divisions etched on the glass, are in the longest cases 18 inches in length. These he calls generating thermometers; and as no thermometer is constant in wide ranges, and at different times, he has other thermometers, smaller, and with only a portion of the scale from freezing to boiling; and prefers to use a special instrument for a special temperature.

The first practical difficulty is the equality of the bore of the tube: round bores are most even, but flat ones are easy to read off. In either case, care should be taken to pick out one with no sudden irregularities. To examine into the quantity of these, portions of the columns must be broken, and passed along the tube, first with one length of column, bisecting the extent of the scale, then trisecting, and so on, until every tenth or every fifth division has been tested. A little skill is required to continue to break off portions of the column without the application of a lamp to the bulb, as has previously been practised; and consists in dexterously reinverting the thermometer, which has just been turned downwards, and so bring the vacuum bubble, which will thereby have been formed in the bulb, to the neck of the tube.

Exceeding pains are then taken, in determining the freezing and boiling points, that the pounded ice in the one case, and the boiling water in the other, are neither above nor below their natural temperatures; but even when this is accomplished there arises the greater difficulty still, that heat seems to produce two sorts of expansions on bodies, viz., the ordinary, or that which ceases with the increase of temperature, and may be called the periodical expansion; and another, which may be called a secular expansion, much smaller in amount than the other, but continuing to exist days, or weeks, or months, according to the bulk of the article acted on.

For strict purposes, therefore, to determine correctly temperatures below boiling, the thermometer should be boiled just previous to being used. But to avoid this trouble, Mr Sheepshanks prefers, for noting ordinary climate temperatures, to have a thermometer marking only to about 70° to 80° Fahr., compared from time to time with one of the generating thermometers, and having its freezing point occasionally tested. Thus avoiding in any one instrument the application of any exceeding variations of temperature.

This secular change probably affects the glass of the bulb more than the mercury contained therein, and is equally present in every metal, and indeed all substances, greatly to the confusion of our attempts to construct standard scales for exact scientific purposes. The age of the bar, and its former experiences, now seem to be elements in determining its length, in addition to the temperature at the

moment.

The old custom of making measuring-rods of wood was necessarily exploded before the advancing requirements for accuracy,

when it was found that, in addition to expansion from heat, which could be measured, there was other expansion from moisture, which could not be measured accurately, and other alteration still from some sort of working or reaction of the late organic forces, which had vivified the wood, and made the tree, and are more difficult than ever to examine into, and seem to defy all our means of measuring their quantity and computing their effects. While bone or ivory, anything in fact which has had life in it, is as little to be trusted as wood.

Recourse was then had to metals, and men revelled in the fancied simplicity and certainty of the corrections to be applied to deduce the true length of a bar at any temperature. Bars of all metals, and in the state of metal, cast or wrought, hammered or rolled, round, flat, thick, thin, hollow, and solid, were all indifferently used: the thermotic expansion being ascertained in each case, by trying the length first in a freezing mixture, then in boiling water, and taking of the difference so found, as the correction due to 1° Fahr.

But now it is found by close microscopic measurements, that according to the degree to which the particles of the bar were distressed in the metallurgic operations of rolling, hammering, &c., so will it have a greater tendency to return, though slowly and through long intervals, to some former shape. And as we cannot ascertain all the blows and severe trials which the bar may have undergone in its process of formation, or probably correct for them, if we did, for the effects will vary with every different metal and every variety of each metal, we can only eschew all recently manufactured bars, and prefer cast to wrought metal.

Next it has been ascertained that no metal expands uniformly with the mercurial thermometer, and therefore the making the correction equal to so many parts of the whole expansion, as the thermometer should be above 32° F., is by no means true for points between 32° and 212°.

And lastly if the bar be heated up to 212°, it will be found not to come down again at once on cooling to its former length at 32°. As therefore so high a temperature is unnecessary, because we never have to use the rods, or to make measurements with them in an atmosphere of that temperature, the once favourite plan of boiling or roasting bars, so as to get their expansion indicated to a great extent, is now given up; and the better method is adopted of leaving the bars altogether to themselves and to nature. They are allowed to take any temperature that they please under the usual changes of climate; their lengths are carefully watched under all those slightly varying alterations of natural heat; observations are greatly multiplied; and equations of condition at last bring out the true law of expansion.

SCIENTIFIC INTELLIGENCE.

METEOROLOGY.

1. The Climatology of Arctic America in reference to the fate of Sir John Franklin.—“ The idea of a cycle of good and bad seasons has often been mooted by meteorologists, and has frequently recurred to my thoughts when endeavouring to find a reason for the ease with which at some periods of Arctic discovery navigators were able to penetrate early in the summer into sounds which subsequent adventurers could not approach, and to connect such facts with the fate of the discovery ships. But neither the periods assigned, nor the facts adduced to prove them by different writers, have been presented in such a shape as to carry conviction with them, until very recently. Mr Glaisher, in a paper published in the Philosophical Transactions for 1850, has shewn, from eighty years' observations in London and at Greenwich, that groups of warm years alternate with groups of cold ones, in such a way as to render it most probable that the mean annual temperatures rise and fall in a series of elliptical curves, which correspond to periods of about fourteen years, though local or casual disturbing forces cause the means of particular years to rise above the curve or fall below it. The same laws doubtless operate in North America, producing a similar gradual increase, and subsequent decrease of mean heat, in a series of years, though the summits of the curve are not likely to be coincident with, and are very probably opposed to those of Europe, since the atmospherical currents from the south, which in a period raise the annual temperature of England, must be counterbalanced by currents from the north or other meridians. The annual heat has been diminishing in London ever since 1844, according to Mr Glaisher's diagram, and will reach its minimum in 1851. It can be stated only as a conjecture, though by no means an improbable one, that Sir John Franklin entered Lancaster Sound at the close of a group of warm years, when the ice was in the most favourable condition of diminution, and that since then the annual heat has attained its minimum, probably in 1847 or 1848, and may now be increasing again. At all events, it is conceivable that, having pushed on boldly in one of the last of the favourable years of the cycle, the ice, produced in the unfavourable ones which followed, has shut him in, and been found insurmountable; but there remains the hope that if this be the period of the rise of the mean heat in that quarter, the zealous and enterprising officers now on his track will not encounter obstructions equal to those which prevented their skilful and no less enterprising and zealous predecessor in the search from carrying his ships beyond Cape Leopold.”—Sir John Richardson.

2. Atmospheric distribution of Iodine.-M. Chatin, the disco