gross vapours, floating near the surface of the earth.

Q. How is it formed P

A. By vapours raised from the earth, which meet, at their first entrance into the atmosphere, with cold sufficient to condense them considerably; their specific gravity being thus increased, their ascent will be stopped at some particular hight, and they will either remain suspended for some time, or return back in a kind of drizzly

rain.

When these vapours are very light and subtile, and become condensed by the coldness of the night before they arrive at any considerable hight, they return back in imperceptible drops; and form what is called dew.

Fogs are only low clouds, or clouds in the lowest region of the air; and clouds are nothing more than fogs raised on high.

OF WATER SPOUTS.

Q. What is a water spout?

A. It is a large collum of water rising in a spiral form from the agitated ocean, with a frightful rushing noise, to a vast hight in the air, and there diffusing itself as it were over the concave of heaven, in dark impen etrable clouds.

Q. What is the cause of this phenomenon ?

A. Dr. Franklin ascribes it to the same cause which produces whirlwinds; namely, the rarefaction of the air: and the circumstance of its seldom appearing but in warm climates, certainly favours this hypothesis.

Q. Of what use are water spouts P

A. They seem to be intended by the Great Author of nature, to supply the earth with moisture after being exhausted by the heat of the sun.

Q. Do they often occur?

A. Yes, in the vicinity of the equator they are very frequent, and would often endanger or destroy ships, were not means found to reduce them before their very near approach. A water spout is readily destroyed by firing a cannon-shot through it, which breaks and lets it down.

OF EARTHQUAKES.

Q. What is an earthquake?

A. A tremendous agitation of some considerable part of the earth, attended with a noise like thunder; and frequently with an eruption of wind or smoke, water or fire; and is undoubtedly the greatest and most formidable phenomenon of nature.

Q, Whence the cause of these terrible phenomena ?

A. Those of a superficial kind may have an

electric origin; for, when a part of the earth is in a highly electrified state, the approach of a non-electric cloud will produce a sudden discharge, and occasion a violent commotion in the earth to many miles in compass. The principal agent of those that are interior and more tremendous, is subterraneous fire.

Q. Please to explain those of subterraneous origin ?

A. The earth abounds with subterraneous caverns, canals, and veins, some full of exhalations, and others full of water; and some parts replete with nitre, sulphur, bitumen, &c. which produce fire: hence, it is easy to conceive the terrible effects which may be occasioned from such confined air or water, when acted upon and greatly rarefied by fire; especially if it be considered, that the expansive force of steam is twenty-eight times. greater than the force of gunpowder.

OF VOLCANOES.

Q. Whatare volcanoes?

A. Volcanoes are burning mountains, which emit flame, ashes, cinders, stones, liquid sulphur, and other substances. There are many of them dispersed in all the quarters of the world: the principal of those in Europe, are Etna, or Gibel, in Sicily; Vesuvious, in Naples; and Hecla,

D

in Iceland. It is owing to those vents of subtert raneous fires, that the effects of earthquakes are more frequent and dreadful.

OF THE TIDES

Q. What is meant by the tides?

A. Two periodical motious of the waters of the sea, called the flux and reflux, or the flow and ebb.

Q. Please to explain these motions ?

A. The sea is observed to flow from the equator toward the north and south poles, for about six hours; in which motion, or flux, the sea gradually swells; so that, entering the mouths of rivers, it drives back the river waters towards their source; after a continual flux of six hours, the sea seems to rest for about twelve minutes ; and in this state it is called high water. When this pause is over, the ebb commences, and the sea retires back again, from the poles to the equator, for six hours more; in which time the water sinking, the rivers resume their course towards the sea; after this reflux the sea again rests another twelve minutes; and in this state it is called low water.

Q. How are these phenomena accounted for?

A. They are occasioned by the attraction of the moon, which extends to the earth in so powerful

a manner as to draw up the waters of the ocean in a heap immediately beneath the moon; while the waters on the opposite side of the earth, being feebly attracted are very light, and the neighbouring waters pressing toward that place, they swell into a heap pointing to the opposite part of the heaven. Thus does the moon, in once going round the earth in 24 hours, produce two tides, or swells, and as many ebbs.

Q. What are the causes of the tide rising much higher at one time than another?

A. The tides are highest about the new and full moon, and are called spring tides; for at these times the action of both the sun and moon are united, and draw in the same straight line, by which means the waters are more elevated; and this elevation is further increased the nearer those two luminaries are to the equator; consequently the highest spring tides are in March and September. The lowest tides are about the first and third quarter of the moon, and are called neap tides; for at those quarters the sun and moon act contrariwise, the sun raising the waters at the point where the moon causes them to be lowest; so that these tides are only occasioned by the difference by which the attraction of the moon, which is nearest the earth prevails over that of the sun.

Q. Whence proceed their other irregular motions?