When M. Richer visited Cayenne, he found a clock he then possessed, of par ticular excellence, which had gone per fectly true at Paris, lost daily two minutes and twenty-eight seconds ; the situation of the island is about five degrees from the equator, and although the heat of a climate lengthens pendulums, and im pedes their motion, yet that of Cayenne was by no means sufficient to produce so considerable a difference, which cannot otherwise be accounted for than by ad mitting less pressure of gravity to have caused it. In the revolution of the earth, its parts recede from the axis, and the equatorial particularly, consequently the polar press internally, and raise the for mer, till an equilibrium occurs ; hence the form of an oblate spheroid, the short er axis of which passes through the poles. Pursuing the lights afforded him by na ture in a superior degree, Newton cal culated the different diameters, and found that the equatorial exceeds the polar 34 miles and one-fifth. This assertion was combated by several philosophers on the continent, but it was fully confirmed sub sequently, by the admeasurements and observations of two deputations of mathe maticians, who visited the vicinity of the northern and southern poles in 1735, and agreed in pronouncing them flattened, making the difference between the diame ters as 266 to 265, or as 179 to 178. Many calculations of profound subtlety have since been made, but as most of the cal culators contradict each other, too much reliance ought not to be placed on either ; those may be fbund in various publica tions, and particularly in the Philosophi cal Transactions, to which brevity com pels us to refer the very curious reader.
The magnitude of the earth is subject to the same uncertainty as the exact figure of it ; but repeated. endeavours have been made to ascertain it with some degree of precision. According to Dio genes Laertius, Anaximander was the first who attempted this difficult task ; it may be supposed with no great success, as be lived 550 years before the Christian mra, though his result was adopted till the period when Erastosthencs flourish ed. Aristotle, in speaking of this subject, says, mathematicians make the circuit of the earth 40,000 stadia, probably includ ing the measurement of Amximander. Certain Arabian philosophers, by the command of their monarch Almaimon, afterwards proceeded to the plains of Mesopotamia, where they went through the process then best known, and found that the circumference of the globe was from 20,160 to 20,340 miles.
Professor Snell, of Leyden, measured considerable distances between the paral lels about 1620, and thus found one de gree amounted to 19 Dutch miles, and the whole circumference to 6,840 miles.
Richard Norwood measured the space between London and York with a chain, fifteen years afterwards, and on the 11th of June, 1635, old style, he took the sun's altitude at the meridian, with a sextant of five feet radius, and found a degree of 69 miles, one half, and 14 poles, whence he inferred that the diameter of the earth is about 7,966 miles, and the circuit 25,036 miles. This measurement, though far su perior to those of the ancients, was tried by several French mathematicians, who suspected some slight errors, by the King's command, with a quadrant of feet radius, French measure, when they ascertained a degree consisted of 542,360 feet. M. Cassini, jun. acting under the same authority, used a quadrant of 10 feet radius, in 1700, with which he ob tained the latitude, and one of 34. feet for taking the angles of the triangles, by which experiment he found the degree to be nearly 69} English miles.
From these and other attempts of a si milar nature, to obtain the length of one degree of the meridian which is to be multiplied by 360, the following mean is generally adopted.
The earth's circumference, 25,000 miles. The diameter, 7,957i.
The superficies, 198,944,206 square miles.
The solidity, 26,393,000,000 cubic miles.
It is conjectured, besides, from the measurement of the most approved maps, that the unexplored portions of the earth and seas contain 160,522,026 square miles, the inhabited part of the former 38,922,180,thusdivided,Europe 4,456,065, Asia 10,768,823, Africa 9,654,807, and America 14,110,874.
The attentive and skilful observer of the works of nature, whether when em ployed in examining the most wretched or the most sublime, will find that judg ment, and infinite wisdom and ingenuity, has equally prevailed throughout. Can it then be supposed for a moment, that the internal parts of the earth we inhabit has received less attention from the Crea tor, than those objects which are under our immediate and unimpeded inspec tion ? Were it possible to entertain a thought so erroneous, we possess strong proofs to the contrary, which convince us that order and regularity reign beneath us in the same degree as around us. Before
the industry, or, more properly speaking, the avarice of man, had led him to pene trate as far as his limited powers will per mit towards the centre, he had but few opportunities of ascertaining, and that only from analogy, how the different strata of the earth was disposed, and connected or held together by the vast masses of atone, which may be called the bones of this vast body. As scientific men were gradually admitted to the knowledge of the secrets of the earth by the exertions of the miner, in the same proportion did ' all ideas of a chaos vanish, and we are now convinced, though Their excavations are mere punctures in the globe, that, were it possible to penetrate through, it would tend to prove that self-existing causes, originating immediately from the Creator, are constantly employed in preserving the whole from derangement, and what we term decay, which, in truth, is simply a change of form, and not annihilation. The celebrated miner, Agricola, was the first who recorded the internal proper ties of the earth, between whose time and that of Werner some discoveries were made as to its structure ; Lehman formed the idea of primitive and secondary clas ses of mountains. Cronstad conjectured the age of several mineral repositories. Hamilton, Dolomieu, and Spallanzani, have gone to very successful and satisfac tory lengths in ascertaining the opera tions of volcanos, the nature of the ma terials which support them, and the sub ' stances they eject. Saussure has increased eur knowledge of rocks, Williams of the • independent formation of coal, and Wer mer has profited by every preceding ob servation, and, possessing a cultivated ge nius of his own, united them into a sys tem,which approaches nearer to the truth than the nature of the subject would lead us to expect. Unfortunately, the labour and expense of penetrating to any great depth into the earth ever has, and ever must, limit our knowledge of the extent of strata, and its similarity in different latitudes ; but from the opportunities al ready afforded by mines, we arc led to conclude that those lines of matter spread through vast spaces, if not throughout the globe ; many theories have been attempt ed, to account for their varieties and ca pricious elevations and depressions from a horizontal direction. Dr. Woodward, who deeply considered the subject, sup poses all the terrestrial masses disposed in strata to have been dissolved by the wa ters of the deluge, which subsiding, the most ponderous fell to the bottom, and the rest settled in gradations suited to their specific weights. This solution na turally disposes the strata uniformly ho rizontal, and he accounts for the breaks in the lines and fissures every where ob servable, by the action of volcanos, earth quakes, &c. &c. Buffon's fancies of cor ners torn from the sun by comets, and the earth lignified by fire, barely deserve notice, and make a disgraceful contrast with Woodward's ingenious conjectures. The surface of the earth is known by every enlightened person to be composed of a confused mass of vegetable, and, in some slight degree, of animal substances, below which, Jameson says, there are four different kinds of structure : " The first is that which is 'to be observed in hand specimens ; it is the smallest kind of structure, and occurs in what are termed mountain-rocks or stones. The second kind of structure, or that of moun tain-masses, is more on the great scale, and is not to be observed in hand speci mens, but only in single masses of rock. To this structure belongs stratification, and the seams of distinct concretions. The third kind of structure is that of rock formations, or those great masses of which the crust of the earth is compos ed. To examine this kind of structure, we must traverse considerable tracts of country. The fourth kind of structure is that of the earth itself, which is formed by the junction of various formations. To examine this structure, we must travel through many countries." When, In passing through long tracts of land, we observe loose rocks, firm rocks, clay, sand, &c. &c. in succession, in those instances the strata of the earth lay almost perpendicular, in large masses of rocks, which present nearly a plain front, the inclination of the strata is dis tinctly visible, and in some cases their agreement with others opposed to them demonstrate, that they have been se parated by some convulsion of the earth.