OPTICS,

Q. What are optics?

A. A science explaining the nature and laws of vision: whether natural, as performed by the eye; or, artificial, as effected by instruments.

Q. How is vision produced?

A. Vision, or the act of seeing by the eye, is performed by rays of light, reflected from an object, and received in at the pupil; which rays are refracted in their passage through the coats and humours to the retina, and being thence conveyed, by the optic nerve, to the common sensorium in the brain, the luminous object is perceived by the mind.

Q. What are the other tenefits of this science?

A. Besides explaining the manner in which vi. sion is performed in the eye, it treats of sight, in general; explains the several modifications which the rays of light undergo in the eye, and why some can only see a short, and others a greater, distance; shows why objects appear sometimes greater, and sometimes smaller; sometimes distinct, and sometimes confused; sometimes near, and sometimes remote: and accounts for the production of light, colours, &c. All the rules of perspective have their foundation in optics.

ASTRONOMY.

Q. What is Astronomy?

A. A mixed mathematical science; teaching the knowledge of the celestial bodies, their magnitudes, motions, distances, periods, eclipses, and order.

Q. What is the use of this science?

A. By knowledge derived from astronomy, not only the size of the earth is discovered, the situation of countries ascertained, trade and commerce carried on to the remotest parts of the world, and its various products distributed for the health and comfort of mankind; but, our very faculties are enlarged with the grandeur of the ideas it conveys; our minds, exalted, above the low-contracted prejudices of the vulgar; and our understandings, convinced of the existence, power, and goodness, of the Supreme Being; who carries on the wonderful harmony and connexion observable throughout the solar system.

Of the Solur System.

Q. What is understood by the solar system?

A. The sun, with the planets and comets which move round him as their centre.

Q. Give some particulars of the Sun?

A. The Sun, an immense globe of fire, is fixed in the centre of the system, having a central motion only about his own axis, in 25 days 6 hours; as is evident by observing the black spots seen on his disk or surface. He is about 763,000 miles in diameter; is nearly one million of times larger than the earth; and dispenses light and heat to all the planets and comets revolving round him.

Q. What are the planets?

A. They are opaque, spherical bodies; having no light of their own, but shining by the reflected light which they receive from the Sun. That side of them, only, is illuminated, which is turned towards him.

Q. How many planets revolve round the Sun?

A. Seven: Mercury, Venus, the Earth, Mars, Jupiter, Saturn, and Herschel. These are called primary planets; four of which are attended by satellites or moons, called secondary planets; which respect the primary as their centre of motion, and revolve round thern as the primary do round the Sun. Each primary planet describes a large orbit, pearly

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