When these causes are numerous and very vi. olent, accompanied with lightning and thunder, the wind becomes so furious and terrible, that it overthrows houses, rocts up trees, and destroys every thing in its course. This is denominated a hurricane.

The velocity of wind, in what is termed a gentle breeze, may be from four to six or eight miles an hour; a strong breeze or brisk wind will travel perhaps from ten to fifteen miles an hour; and a hurricane or tempest probably not less than fifty or sixty miles.

The air is often observed, in different regions, to move in contrary currents; and this, almost, always, previous to thunder.

Q. What are clouds?

A. A quantity of condensed vapours, suspended in the atmosphere.

Q. How are they formed?

A. From a collection of watery particles, raised from the earth by solar and subteraneous heat:, the particles, at their first rise, are too minute and separate to be perceived; but, meetirs, in their ascent, with a greater degree of cold, they are condensed and their parts united, so as to reflect light, and become visible.

Q. At what height, do you suppose the clouds to be suspended:

A. From about a quarter of a mile to two miles; according to their specific gravity, and to the elasticity of the atmosphere. They are frequently visible below the tops of very high hills.

Q. Whence, are their various forms and colours?

A! Their figure results from their loose texture; changing into any form'arcording to the different curients of the air: and their colour is owing to their particular situation with regard to the sun, and the different reflections of his lght.

It appeurs from the observable motion of the clouds, that there are different currents in the air, at she same time, and in the same quarter, under one another.

OF THE RAINBOW

Q. What is a rainbow?

A. A meteor in the form of an arch, exhibited in a rainy atmosphere, opposite to the sun.

Q, Of what colours, does it consist?

A. They are, beginning from the upper part, red, orange, yellow, green, blue, indigo, and violet; which are called the seven primary colours: for, all other colours are composed of some of them.

Every ray of light is a compound body; consisting of these seven colours: but mixed in such proportions, as to produce the appearance of white

As these colours possess different degrees of frangibility. they are easily separated. Let a ray of light pass throngh a drop of water, and the violet will suffer a greater refraction than the red; consequently, they will be separated.

Q. How is the rainbow formed!

A. It is made by the rays of the sun being refracted in the drops of falling rain, and thence reslected to the eye of a spectator, who is between the sun and the rain.

Q. How are the various colours produced?

A. By the different refractions of the rays, transmitted to the eye from several drops; one higher than another the rays least refracted producing red; those most refracted, violet; and the intermediate ones, the other colours, in the order before mentioned.

R. I have sometimes observed two bows, one above the other; how are these accounted for?

A. The interior and stronger one is produced by one reflection; the exterior and fainter, by two: when the latter is visible, its colours lie in a contrary order to the other.

The doctrine of the rainbow is confirmed by an easy esperiment: for, upon hanging up a glass globe full of water, in the sunsline, and viewing it in such a position, as that the rays, which come from the globe to the eye, may, with the sun's rays, include an angle of about 490, the spectator will see a full red colour in that side of the globe opposite the sun: and if that angle be made a little less by depressing the globe or raising the eye, the other colours yellow, green, and blue, will appear, successively: but if the angle be made about 50°, there will appear a faint red colour in that side towards the sun; and if the angle be made greater, the other colours will be seen, in their regular order.

Q. How is the lunar rainbow formed?

A. Exactly in the same manner as the other; by the beams of the moon falling upon the bosom of a shower.

Q. How is that lucid ring, called the halo, which we sometimes see diffused around the moon, ac counted for?

1. As it always appears in rainy or frosty weather, we may suppose it occasioned by the refraction of light, in the watery, or frozen particles, of the atmosphere.

OF HAIL,

Q. What is hail?

A. An aqueous concretion, generally round, but sometimes angular, triangular &c. according to the suddenness of its first formation, and the degrees of cold through which it passes in its descent.

Q. How is it produced?
A. It is supposed to be formed in the high re..

gions of the air; where the cold is intense, and where the electric matter is very copious: for, in these circumstances, a great number of particles of water being brought near together, are frozen, and in their descent collect other particles: so that the density of the substance of the hailstone decreases from the centre; this being formed first in the upper regions, and the surface being collected in its falling through the lower.

OF SNOW.

Q. How is snow produced?

A. It is formed in the middle region of the atmosphere; of particles of water there congealed, and to which, similar particles unite and still accumulate as they descend through a cold air, till they fall to the earth in what we term flakes of

Snow.

Q. Why are those flakes so light?

A. Their lightness is owing to the extent of the surface, in comparison with the matter cotained under it; as gold itself may be extended in surface till it will float upon the least breath of air.

Q. What is the cause of their whiteness?

A. The particles of ice that compose these flakes, being solid, transparent, and differently arranged, reflect the light from every part.

Q. Of what benefit is snow to the earth?