Imágenes de páginas
PDF
EPUB

from the time of his passing any particular 'meridian to the time of his returning to the same meridian. The opendulum usually employed is of such a length as to divide the mean astronomical day into equal parts, called 8 seconds; 60 of these parts make a minute, 60 minutes make an hour, and 24 hours complete the day. .

As the apparent motion of the sun carries him eastward among the fixed stars, the time that elapses between his passing the meridian and his returning to it again, is longer than the time that 'intervenes between two successive passages called 'transits of any particular star. This latter period is the exact time of the earth’s revolution on its axis, and is called a 'sidereal day; it is about 23 hours, 56 minutes, 4 seconds, in length.

The motion of the earth on its axis being perfectly uniform, the length of the sidereal day is always the same. This is not the case however, with respect to the astronomical or solar day, which is affected by the unequal motion of the sun, and by the obliquity of the ecliptic At the summer solstice, towards which the sun's motion in the ecliptic is slowest, the solar day is more nearly equal to the sidereal day than at the winter solstice, when the sun's motion is quickest.

The motion of the shadow on a sun-dial marks out the time, as measured by the sun's motion in the ecliptic; but if the sun moved uniformly in the 'equator, at such a rate as to complete the annual circuit in the heavens in the same time as he does by his actual motion in the ecliptic, time measured by his motion would then correspond with that of a well-regulated clock.

The difference between the time shown by the sun-dial and that shown by the clock, is called the equation of time.

1. Vide Root.

2. Vide page 61.

3. 24 X 60 X 60=86,400.

GREECE. Brief Sketch of its Early History. WHEN the 'human race was scattered from the tower of Babel, it is supposed that Japheth, Noah's youngest son, travelled from Asia into Europe. As Greece lay nearer to the land of Shinar than the other parts of Europe, it was probably settled first.

Cecrops, an Egyptian, seems to have been the first who 'introduced 'civilization among the 'Greeks. He came with a number of his countrymen, and founded the city of Athens. This event took place about 1556 years before the Christian era.

Thirty or forty years after, Cadmus came from Phenicia, and built Thebes. He was one of the greatest ? benefactors of the Greeks, for he taught them the cultivation of the vine, the 'manufacture of metals, and the use of the alphabet. The country then consisted of a number of small kingdoms.

Twelve of these little kingdoms, or states, soon united themselves into a 'confederacy. Their deputies held a meeting twice a year in order to consult respecting the welfare of the country. They were called the council of the Amphictyons. By means of this council, the different states were kept at peace with each other, and were united against foreign enemies. One of the famous events of Grecian history was the Argonautic expedition. It is said that a prince named Jason, with a company of his friends, sailed to Colchis, which lay eastward of the Black Sea. Their object was to find a wonderful ram with a fleece of gold; but the whole story is supposed by some to be a fable.

1. Vide Root. 2. The Greeks obtained their knowledge from the learned men of Asia and Egypt, and became the instructors of the Romans, and through them of the nations of Europe. At this early period lived Hercules, Theseus, Jupiter, Saturn, and other distinguished persons, who were subsequently worshipped by the Greeks, as gods or demi-gods. The whole nation was directed by an oracle at Delphos, where a priestess, sitting over the mouth of a cave, pretended to foretell events, and to give answers from Apollo.

The Trojan war was still inore famous than the expedition in search of the golden fleece. Troy was a large city on the Asiatic side of the Hellespont, which is now called the Dardanelles. Paris, the son of the Trojan king, had stolen away the wife of Menelaus, a Greek prince. All the Grecian kings combined together to punish this offence. They sailed to Troy in twelve hundred vessels, and took the city after a siege of ten years. This event is supposed to have occurred eleven hundred and ninety-three years before the Christian era.

One of the principal states of Greece was called Sparta or Lacedemon. It was founded by Lelex, 1516 B.C. It received a code of laws from Lycurgus, who lived nearly nine centuries before Christ. He was strict and severe, but wise and upright. Many of his laws, however, belonged to a savage, rather than a civilized nation.

Athens had subsequently two celebrated lawgivers, Draco and Solon. The laws of Draco were so extremely severe, that they were said to be written with blood, instead of ink: he punished even the smallest offences with death. His code was soon abolished. Solon's laws were much milder. Athens was at this time a republic, which is a government by the people themselves; but soon after Solon had made his laws, the 'supreme power was usurped by Pisistratus, an ambitious citizen. He and his sons ruled Athens fifty years.

GEOGRAPHICAL.-Area, 16,000 square miles. Population, 812,000.

How is Greece bounded ?
Divide it into geographical parts, and write the names of its peninsulas, islands,

isthmuses, capes, and mountains.
CHRONOLOGICAL.-Homer born in B.C. 900. Golon, the lawgiver, B.O. 643.

Lycurgus gives laws to Sparta, 884. Battle of Marathon, 490.

GEOLOGY.

Crust of the Globe. The crust of the globe is composed of two great classes of rocks, one of which consists of a series of beds of stone of different kinds, lying upon one another in a certain determinate order of succession, called Strata ; the other of a class of stones distinguishable from the strata by peculiar mineral composition, by never containing pebbles, or the remains of animals or plants, and by never being arranged in parallel layers, from which last character they have been denominated the Unstratified Rocks.

It is quite evident, that the mode of formation of the two must have been totally different. While the strata, by their parallel arrangement, by the pebbles of preexisting rocks, and by the remains of living bodies which they contain, demonstrate that they must have been formed under water, by deposition from the surface downwards,—the whole characters of the unstratified rocks equally prove, that they must have come to the surface from the interior of the earth, after the deposition of the strata; that is, that they have been "ejected among the strata from below in a melted condition, either fluid or in a soft yielding state.

In every case the unstratified rocks lie under the stratified. This order has never been reversed, except where they have been protruded through a strata.

1. Vide Root. 2. The elementary substances which compose the varieties of stones or rocks are few, consisting of only the four earths, silex, clay, lime, and magnesia, with oxide of iron, carbon, and sulphur. The silex forms probably nine. teen-twentieths of the mass of our globe.

The following terms are generally used in describing geological substances: compact, when without any distinguishable parts or divisions; earthy, comprised of mi. nute parts resembling dried earth; granular, composed of grains; fibrous, when composed of long and minute fibres; radiated, when the fibres are broader and flattish, and very distinct; lamellar or foliuted, when composed of thin plates laid over each other ; porous, when penetrated by pores; cellular or vesicular, when the pores have rounded bladder like cavities, as in some lavas; slaty, when composed of 4 bin leaves or laminæ.

STRATIFIED Rocks. -The lowest members in the order in which the stratified rocks are placed one above another, are distinguished by the great predominance of hard slaty rocks, having a crystalline or compact texture, but chiefly by this circumstance, that they have not been found to contain any fragments of pre-existing rocks, or the remains of organized bodies. On this account they have been called the 3 PRIMARY Strata, as if formed prior to the existence of animal life, and as containing no evidence of other rocks having existed before them. · The Secondary Rocks comprehend a great variety of different beds of stone, extending from the primary strata to the chalk, which forms the upper or most recent member of the division.

These rocks consist of an extensive series of strata, of limestones, sandstones, and clays, all of which contain either rounded fragments of pre-existing rocks, or organic remains, or both; and each group, and all the subordinate members of the groups, are distinguishable by characters of great constancy and certainty, derived from the peculiar nature of the included fossils.

The Tertiary Rocks consist of a great variety of strata of limestones, sandstones, clays, and sands, which have distinct characters, and have been united in several groups. In them we first discover the remains of land quadrupeds and birds; and bones of mammalia are most abundant in the beds nearest to the surface.

Thus the whole series of strata, of which the crust of the globe is composed, is divided into the Primary, the Secondary, and the Tertiary.

3. There are seven sets of primary formations : granite, gneiss, mica-slate, clay-slate, newest primitive porphyry, sienite, newer serpentine. 4. Between the primary and secondary are placed the four sets of rocks-Greywacke, transition limestone, transition trap, transition flint-slate, called the transition rocks.

« AnteriorContinuar »