Abbildungen der Seite

mode of education to limit the reading of youth to books bu a few particular subjects ; so that when young men are ushered into the world, many and even most of them are unacquainted with even the appropriate terms used in other sciences.

But the advantages of a more diffusive system of instruction will not rest here--By reading frequently and repeatedly, passages containing just rules and principles, even above the comprehension of young minds, the pupils will learn many of them by heart, and bear the impressions into future life ; by which means, wben their understandings are more matured, they will be enabled to direct, to useful purposes, the principles with which they had stored their minds in school. In this manner, useful rules and facts, acquired in youth, like feed fown in a good foil, will produce their fruit in riper years, and increase the harveft of knowledge and improvement, to enrich the community.

In the language, the author has aimed to use a style, which is plain without being vulgar; and technical, without need. less obscurity.

In every part of this work, occasions frequently occur of deducing moral and piqus reflections from the subjects treated. On such occasions, special care is taken to lead the mind of the reader, from a consideration of the order, beauty and fitness of all parts of nature, to contemplate the neceffity and certainty of the existence of a Creator, of infinite power, wisdom and goodness. This mode of employing natural philosophy in the service of religion and piety, has been practiced by the ableft authors and beft men in all ages-it furnishes powerful aids to that firm belief in the being and providence of God, and that pious veneration for his character and attributes, which are the prime ornaments of a wise man and a good citizen.

[ocr errors]

Elements of Useful Knowledge.



Of the Solar System.
THE solar system consists of the sun, and the stars

or globes which move round it, called planets. Of the Sun. The sun is an immense body, placed near the center of the system, diffusing light and heat to all the planets. Its diameter is eight hundred and ninety thousand miles.

Planets. The primary planets, exclusive of those which liave been lately discovered, are seven ; Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Herschel. * To these may be added, Ceres, Pallas and Hercules, which have been lately discovered. All the planets revolve about the sun, and receive their light and heat from that resplendent luminary.

Secondary Planets. The secondary planets are smaller orbs which revolve round the primary planets, as the moon, which moves round the earth in about twenty nine days. Jupiter has four moons, or fattellites, and Saturn, seven, which constantly move round those planets.

The planet Herschel has fix sattellites.

Mercurs. Mercury is three thousand two hundred and twenty miles in diameter, and revolves round the sun in about eighty eight days, at the distance of nearly thirty seven millions of miles.

* Pronounced Herfiel.


Venus. Venus is about seven thousand, seven hund red miles in diameter, and revolves round the fun in about seven months and a half, at the distance of nearly fixty eight millions of miles.

The Earth. This globe which we inhabit, is a planet of nearly eight thousand miles in diameter and twenty five thousand miles in circumference. Its distance from the sun is about ninety five millions of miles, and its revolution round the sun makes our year, or three hundred and fixty five days, and nearly fix hours.

Mars. Mars is in diameter four thousand two hună dred miles. Its revolution about the sun is performed in one year and three hundred and twenty one days, at the distance of one hundred and forty four millions of miles.

Jupiter. Jupiter is the largest of the planets, haying a diameter of ninety four thousand miles. Its diftance from the sun is calculated to be nearly four hundred and ninety five millions of miles, and its revolution round the sun is performed in a little less than

Saturn. Saturn has a diameter of feventy. nine thousand miles. Its distance from the sun is calculated to be nearly nine hundred millions of miles, and its revolution round the sun is performed in twenty nine years and a hundred and fixty seven days. Saturn has two rings and a belt of spots.

Herschel. This planet, which bears the name of its discoverer, who first observed it in 1781, is nearly thirty five thousand miles in diameter; its distance from the fun, one thousand and eight hundred millions of miles, and its revolution about the fun is performed in eighty three years and a half.

Ceres and Pallas. Ceres was discovered by Mr. Pia azzi, at Palermo in Sicily, in the year 1801. "Its diameter is one hundred and fixty two miles. Pallas was discovered by Dr. Olbers of Bremen in 1802 ; its diameter is ninety five miles, and in its revolution it is not confined to the zodiac.

Hercules. In 1804, Dr. Olbers discovered another

twelve years.

planet, which is three times as large as Jupiter, and which, for its magnitude, he calls Hercules. Its diftance from the sun is three thousand and forty seven millions of miles, and its revolution is calculated to be twenty four years. It has seven satellites.

Orbits of the Planets. The planets move round their centers, not in a true circle, but in a figure called an ellipsis, which somewhat resembles the form of an egg.

Perihelion and Aphelion. As the planets do not revolve round the fun in a circle, they approach nearer to the fun in one part of their orbits, than in other parts. That part of the orbit neareft the sun, is called the perihelion ; and the part most diftant, the aphelion.

Laws of planetary motion. The nearer a planet is to the fun, or its center, the faster it moves. Thus Mercury moves much faster than Saturn. So a planet moves more rapidly in its perihelion, than in its aphelion. The earth is nearer the sun and moves falter in winter, than in summer ; hence the summer with us is eight days longer than the winter.

Of Attraction and Repulfion. That principle in bodies which difpofes them to unite and cohere, is called attraction. That principle which disposes them to feparate or recede from each other, is called repulfon. The tendency of a planet towards the center of the fystem, is called its centripetal force ; the power that impels it to recede from the center, its centrifugal force ; and thefe combined are supposed to generate the circular motion of the planets.

Of a Circle. Every circle is divided into three hundred and sixty degrees, a quarter of which or a quadrant is ninety degrees. Every degree is divided into fixty minutes, and each minute into fixty seconds.

Of the Zodiac. Tlie Zodiac is a broad circle or belt in the heavens, containing the twelve figns, or conftellations, most of which are represented by certain ani. mals, by whose names they are called. Each sign comprehends thirty degrees.

Names of the signs. The figns are called Aries,

« ZurückWeiter »