waters situated at the nadir. If we consider the elevation of the waters on each side of the globe to be eight feet, it is evident that the earth must, by the attractive power of the luminaries, have been removed sixteen feet. However incomprehensible this theory is, the difficulties are increased by the application of the same principle to the explanation of spring tides at full moon, when the earth is placed exactly in a line between the two luminaries.

In the year 1799, I published an analysis of a Course of Lectures. I therein attempted to explain the phenomena of the tides, on the principle of the motion of the earth round the centre of gravity of the earth and moon. A similar ex

planation had been surmissd by the learned Dr. Wallis in 1666. I am not aware that he attempted any demonstrations of such an opinion. In the different courses of Lectures I have delivered during a period of near thirty years, when upon the subject connected with the tides, I have invariably attributed them to the result of this motion. In the first place, it will be necessary to premise a few observations as to the centrifugal power of the earth, and the effect produced by this motion as to its form. The figure of the earth is extremely complicated-indeed its exact shape will never be ascertained until the terrestrial arcs are measured in every direction. Although the late accurate surveys of Delambre and Mechain indicate a diminution in the terrestrial degree from the pole to the equator, they likewise evince that the law of this diminution is very irregular, and that its two hemispheres are not equal on each side of the equator; consequently, the earth cannot be a solid of revolution. In the southern latitude of 33 degrees 18 minutes, La Caille found the measure of a degree greater than at 40 degrees 11 minutes north latitude. From these admeasurements it is deduced that the equatorial diameter exceeds the polar axis by 23.7 miles. If we suppose the form of the earth, before it was in motion, spherical, when the motion round its action was induced, the earthy mass not being then in a consolidated state, would, from the laws of centrifugal motion, assume a spheroidal form, and a depression at the poles. This elevation of matter must be one-half the difference of the two diameters, viz. 11.85 miles. But the mean diameter of the earth exceeds the polar axis by the last In order to bring into calculation the actual quantity of matter thus raised by the centrifugal power of the earth, we have only to ascertain the difference between a sphere of 7923.44 miles in diameter, and a sphere of 7911.85 miles, and this difference is to the whole globe as 1 to 220. As the

sum.

mean density of the earth is greater than the density of the elevated portion,-and from the experiments of Maskelyne and Cavendish, we are authorized to consider the increase as one-third, the results will be a near coincidence with that diminution of gravitation under the equator, being estimated from a series of accurate experiments with pendulums to be as 1 to 289. Had the velocity of the earth been 17 times greater, the centrifugal power under the line would have counteracted gravitation, and no such circumstance as weight could have existed at the equator.

The earth does not move in a regular elliptic orbit round the sun, but describes a series of volutes round the centre of gravity between the earth and the moon. As the density of the moon is, to the density of the earth, as 11 to 9-which has been deduced from calculations of the space the moon falls below the tangent of her orbit in a given time—and as the diameter of the moon is 2161 miles, therefore it is, in proportion to the mass of earth, as 1 to 49.22. From these data it is evident that the distance of the moon's centre from the common centre of gravity of the earth and moon is as 39.788 to 1, or 5880 miles from the centre of the earth.

It will hence appear that the earth has a triplicate motion -one round her axis, constituting day and night; one round the sun, constituting the year; and a motion in common with the moon round the centre of gravity.-Dr. Wilkinson.

SHIP-BUILDING.-To give an idea of the enormous quantity of timber necessary to construct a ship of war, we may observe that 2,000 tons, or 3,000 loads, are computed to be required for a seventy-four. Now, reckoning fifty oaks to the acre, of 100 years' standing, and the quantity in each tree to be a load and a half, it would require forty acres of oak forest to build one seventy-four; and the quantity increases in a great ratio for the largest class of line-of-battle ships. The average duration of these vast machines, when employed, is computed to be fourteen years. It is supposed that all the full-grown oaks now in Scotland would not build two ships of the line.

GAS IN CHINA.-In the district of Kea-ting-too, in the province of Sze-chuen, are ancient salt-pits or wells, which no longer afford water, although they have been dug, for that purpose, to the depth of 3000 feet; but, instead, they yield matter for a prodigious quantity of fire, which is applied to use, being, by means of conducting tubes of bamboo, employed to heat the cauldron in which the salt is boiled down. The residue is used to light the streets, and halls, and kitchens, by means of conducting tubes.

THE IRISH SCHOOLMASTER.

No chair he hath, the awful pedagogue,
Such as would magisterial hams imbed,
But sitteth lowly on a beechen log,
Secure in high authority and dread:
Large as a dome for learning seems his head,
And, like Apollo's, all beset with rays,
Because his locks are so unkempt and red,
And stand abroad in many several ways:
No laurel crown he wears, howbeit his cap is baize.

And, underneath, a pair of shaggy brows
O'erhang as many eyes of gizzard hue,
That inward giblet of a fowl, which shows
A mongrel tint, that is ne brown ne blue;
His nose-it is a coral to the view,

Well nourish'd with Pierian Potheen;

For much he loves his native mountain-dew ;-
But to depict the dye would lack, I ween,
A bottle-red, in terms, as well as bottle-green.

And soe he sits, amidst the little pack,
That look for shady or for sunny noon
Within his visage, like an almanack,—
His quiet smile foretelling gracious boon;

But when his mouth droops down, like rainy moon,
With horrid chill each little heart unwarms,
Knowing, that infant showers will follow soon,
And with forebodings of near wrath and storms
They sit, like timid hares, all trembling on their forms.

Ah! luckless wight, who cannot then repeat
"Corduroy Colloquy," or " Ki, Kæ, Kod,”-
Full soon his tears shall make his turfy seat
More sodden, though already made of sod,

For Dan shall whip him with the word of God,

Severe by rule, and not by nature mild,

He never spoils the child and spares the rod,
But spoils the rod and never spares the child,
And soe with holy rule deems he is reconciled.

But, surely, the just sky will never wink
At men who take delight in childish throe,
And stripe the nether-urchin like a pink
Or tender hyacinth, inscribed with woe;
Such bloody pedagogues, when they shall know,
By useless birches, that forlorn recess,

Which is no holiday, in pit below,

Will hell not seem design'd for their distress,

A melancholy place that is all bottomlesse?-HOOD.

CURIOUS METHOD OF SPLITTING ROCKS.-In the granite quarries near Seringapatam the most enormous blocks are separated from the solid rock by the following neat and simple process.-The workmen having found a portion of the rock sufficiently extensive, and situated near the edge of the part already quarried, lays bare the upper surface, and marks on it a line in the direction of the intended separation, along which a groove is cut with a chisel about a couple of inches in depth. Above this groove a narrow line of fire is then kindled, and maintained till the rock below is thoroughly heated, immediately on which a line of men and women, each provided with a pot full of cold water, suddenly sweep off the ashes, and pour the water into the heated groove, when the rock at once splits with a clean fracture. Square blocks of six feet in the side, and upwards of eighty feet in length, are sometimes detached by this method. Such a block would weigh nearly 500,000 pounds.

SCIENCE PERPETUAL.-Monarchs change their plans-governments their objects-a fleet or an army effect their purposes, and then pass away; but a piece of steel touched by the magnet preserves its character for ever, and secures to man the dominion of the trackless ocean. A new period of society may send armies from the shores of the Baltic to those of the Euxine, and the empire of Mahomet may be broken in pieces by a northern people, and the dominion of the Britons in Asia may share the fate of that of Tamerlane or Zengiskhan; but the steam-boat which ascends the Delaware or the St. Lawrence will continue to be used, and will carry the civilization of an improved people into the deserts of North America, and into the wilds of Canada.

AQUEDUCT OF CASERTA.-There is nothing so worthy of a stranger's admiration, in the neighbourhood of Naples, as the magnificent aqueduct which supplies the Royal Palace ; it consists of three rows of arches built the one above the other; the line over which the water passes in the highest conduit is above 1600 feet in length, and its elevation, from the edge to the subjacent valley is 178 feet, the second 27, and the loftiest 43. This is indeed an elevation worthy of the splendid days of ancient Rome. It was begun in 1753, and completed in six years.

WONDROUS EFFECTS OF CHEMISTRY.-Not to mention the impulse which its progress has given to a host of other sciences, what strange and unexpected results has it not brought to light in its application to some of the most common objects! Who, for instance, would have conceived that linen rags were capable of producing more than their own

weight of sugar, by the simple agency of one of the cheapest and most abundant acids?—that dry bones could be a magazine of nutriment, capable of preservation for years, and ready to yield up their sustenance in the form best adapted to the support of life, on the application of that powerful agent, steam, which enters so largely into all our processes, or of an acid at once cheap and durable?—that sawdust itself is susceptible of conversion into a substance bearing no remote analogy to bread; and though certainly less palatable than that of flour, yet no way disagreeable, and both wholesome and digestible, as well as highly nutritive?

HEAT. Why does hay, if stacked when damp, take fire? -Because the moisture elevates the temperature sufficiently to produce putrefaction, and the ensuing chemical action causes sufficient heat to continue the process; the quantity of matter being also great, the heat is proportional.

Why is a tremulous motion observable over chimney-pots, and slated roofs which have been heated by the sun?-Because the warm air rises, and its refractive power being less than that of the colder air, the currents are rendered visible by the distortion of objects viewed through them. Within doors, a similar example occurs above the foot-lights of the stage of a theatre, the flame of a candle, or the smoke of a lamp.

Why are the gas chandeliers in our theatres placed under a large funnel-Because the funnel, by passing through the roof into the outer air, operates as a very powerful ventilator, the heat and smoke passing off with a large proportion of the air of the house. The ventilation of rooms and buildings can only be perfectly effected, by suffering the heated and foul air to pass off through apertures in the ceiling, while fresh air, of any desired temperature, is admitted from below.

ELECTRICITY.—Why is the fireside an unsafe place in a thunder-storm?-Because the carbonaceous matter, or soot, with which the chimney is lined, acts as a conductor for the lightning.

Why is the middle of an apartment the safest place during a thunder-storm?-Because, should a flash of lightning strike a building, or enter at any of the windows, it will take its direction along the walls, without injuring the centre of the room.

TEETH.-M. La Beaume, the medical electrician, has made a very curious discovery, that the accumulation on the teeth, termed tartar, is occasioned by animalculæ, which are visible on microscopic examination. According to this