nitude, than the roughness of an orange hinders it from being esteemed round.

When philosophical and mathematical knowledge arrived at a still greater degree of perfection, there seemed to be very sufficient reason for the philosophers of the last age to consider the earth not trul spherical, but rather in the form of a spheroid. This notion first arose from observations on pendulum clocks, which being fitted to beat seconds in the latitude of Paris and London, were found to move slower as they approached the equator, and at, or near the equator they were obliged to be shortened about one eighth of an inch to agree with the times of the stars passing the meridian. This difference appearing to Huygens* and Sir Isaac Newton, to be a much greater quantity than could arise from the alteration by heat only, they separately discovered that the earth was flatted at the poles.-By the revolution of the earth on its axis (admitting it to be a sphere) the centrifugal force at the equator would be greater than the centrifugal force in the latitude of London or Paris, because a larger circle is described by the equator in the same time; but as the centrifugal force, (or tendency which a body has to recede from the centre) increases, the action of gravity necessarily diminishes; and where the action of gravity is less, the vibrations of pendulums of equal lengths become slower ; hence supposing the earth to be a sphere, we have two causes why a pendulum should move slower at the equator than at London or Paris, viz: the action of heat, which dilates all metals, and the diminution of gravity. But these two causes combined would not, according to Sir Isaac Newton, produce so great a difference as one eighth of an inch in the length of a pendulum, he therefore supposed the earth to assume the same figure that a homogeneous fluid would acquire by revolving on an axis, viz: the figure of an oblate spheroid, and found that the "diameter of the earth at the equator, is to its diameter from pole to pole, as 230 to 229." Notwithstanding the deductions of Sir Isaac Newton, on the strictest mathematical principles, many of the philosophers in France, the principal of whom was Cassini, asserted that the earth was an oblong spheroid, the polar diameter being the longer; and as these different opinions were supposed to retard the general progress of science in France, the king resolved that the affair should be determined by actual admeasurement at his own expense. Accordingly, about the year 1735, two companies of the most able mathematicians of that nation were appointed: the one to measure the degree of a meridian as near to the equator as possible, and the other company to perform a like operation as near the pole as could be conve

A celebrated mathematician, born at the Hague, in Holland, in 1629.

niently attempted. The results of these admeasurements contradicted the assertions of Cassini, and of J. Bernoulli, (a celebrated mathematician of Basil, in Switzerland, who warmly espoused his cause) and confirmed the calculations of Sir Isaac Newton. In the year 1756, the Royal Academy of Sciences at Paris appointed eight astronomers to measure the length of a degree between Paris and Amiens; the result of their admeasurement gave 57069 toises for the length of a degree.

The utility of finding the length of a degree in order to determine the magnitude and figure of the earth, may be rendered familiar to a learner thus: suppose I find the latitude of London to be 511° north, and travel due north till I find the latitude of a place to be 52° north, I shall then have travelled a degree, and the distance between the two places, accurately measured, will be the length of a degree: now, if the earth be a correct sphere, the length of a degree on a meridian, or a great circle, will be equal all over the world, after proper allowances are made for elevated ground, &c. the length of a degree multiplied by 360 will give the circumference of the earth, and hence its diameter, &c. will be easily found: but if the earth be any other figure than that of a sphere, the length of a degree on the same meridian will be different in different latitudes, and if the figure of the earth resemble an oblate spheroid, the lengths of a degree will increase as the latitudes increase. The English translation of Maupertuis' figure of the earth, concludes with these words: The degree of the meridian which cuts the polar circle being longer than a degree of the meridian in France, the earth is a spheroid flatted towards the poles. For, the longer a degree is, the greater must be the circle of which it is a part; and the greater a circle is, the less is its curvature.

The first person who measured the length of a degree with any appearance of accuracy was Mr. Richard Norwood; by measuring the distance between London and York, he found the length of a degree to be 367196 English feet, or 694 English miles; hence, supposing the earth to be a sphere, its circumference will be 25020 miles, and its diameter 7964 miles;* but if the length of a degree, at a medium, be 57069 toises, the circumference of the earth will be 24873 English miles, its diameter 7917 miles, and the length of a degree 69 miles. CONCLUSION.-Notwithstanding all the admeasurements that have hitherto been made, it has never been demonstrated, in a satisfactory manner, that the earth is strictly a spheroid ; indeed,

5280 feet make a mile, therefore 367196 divided by 5280 gives 69 miles nearly, which, multiplied by 360, produces 25020 miles, the circumference of the earth, but the circumference of a circle is to its diameter as 22 to 7, or more nearly as 355 to 113; hence 355: 113:: 25020 miles: 7964 miles, the diameter of the earth.

from observations made in different parts of the earth, it appears that its figure is by no means that of a regular spheroid, nor that of any other known regular mathematical figure; and the only certain conclusion that can be drawn from the works of the several gentlemen employed to measure the earth is, that the earth is something more flat at the poles than at the equator. The course of a ship, considering the earth a spheroid, is so near to what it would be on a sphere, that the mariner may safely trust to the rules of globular sailing, even though his course and distance were much more certain than it is possible for them to be. For which, and similar reasons, mathematicians content themselves with considering the earth as a sphere in all practical sciences, and hence the artificial globes are made perfectly spherical, as the best representation of the figure of the earth.

Of the Diurnal Motion of the Earth.

The motion of the earth was denied in the early ages of the world yet, as soon as astronomical knowledge began to be more attended to, its motion received the assent of the learned, and of such as dared to think differently from the multitude, or were not apprehensive of ecclesiastical censure.-The astronomers of the last and present age have produced such a variety of strong and forcible arguments in favour of the motion of the earth, as must effectually gain the assent of every impartial inquirer. Among the many reasons for the motion of the earth, it will be sufficient to point out the following.

The earth is a globe of 7964 miles in diameter; and by revolving on its axis every 24 hours* from west to east, it causes an apparent diurnal motion of all the heavenly bodies from east to west. We need only look at the sun, or stars, to be convinced that either the earth, which is no more than a point when compared with the heavens, revolves on its axis in a certain time, or else the sun, stars, &c. revolve round the earth in nearly the same time. Let us suppose, for instance, that the sun revolves round the earth in 24 hours, and that the earth has no diurnal motion. Now, it is a known principle in the laws of motion, that if any body revolve round another as its centre, it is necessary that the central body be always in the plane in which the revolving body moves, whatever curve it describes; therefore, if the sun move round the earth in a day, its diurnal path must always describe a circle which will divide the earth into two equal hemispheres. But this never happens

That is, the time from the sun's being on the meridian of any place, to the time of its returning to the same meridian the next day; but the earth forms a complete revolution on its axis in 23 hours, 56 minutes, 4 seconds.