he arctic circle, and the south frigid zone from the south pole to the antarctic circle.

Beyond the 60th degree, and as far as the 7Sth, (which, as M. Malte-Brun remarks, appears to be the limit of the habitable earth in the northern hemisphere,) only two seasons are generally known; a long and rigorous winter, succeeded often suddenly by insupportable heats. The power of the solar beams, though feeble, from the obliquity of their direction, accumulates during the days, which are extremely long, and produces effects which might be expected only in the torrid zone. There have been examples, of forests having been set on fire, and of the pitch melting on the sides of ships. In winter, on the contrary, brandy has been frozen in heated rooms; the earth has been found frozen to the depth of 100 feet; and mercury, congealed in the thermometer, leaves the degree of cold indeterminate. We speak here of extreme cases and of the zone in general. For, in some places, a southern exposure, and the neighbourhood of the ocean, soften the climate to an almost incredible degree. Bergen in Norway, and the whole of the adjoining coast, between 60 and 62 degrees of latitude, has a very rainy winter, but seldom snow or frost-that season of the year is there less rigorous, and requires less fuel than at Craconia, or Prague, or Vienna, in Austria, between the 48th and 50th degrees of latitude. The frigid zone enjoys an atmospheric calm, which is unknown in temperate regions-it has no storm, no hail; scarcely a tempest-the plendours of the aurora borealis, reflected from the snow, dispel the darkness of the polar night. The heat of the sun from his long continuance above the horizon, astonishingly accelerates the growth of vegetation. In three days, or rather three times twenty-four hours, the snow is melted and the flowers begin to blow. The succession of physical zones is not equal in the two hemispheres: for, in the arctic seas, we scarcely meet with the large floating masses of ice before we arrive at the 70th degree, nor the stationary fields, until towards the 75th or 80th degrees of latitude; while, in the antarctic seas, both occur at from 50 to 60 degrees southern latitude. In the island of Terra del Fuego, in that of Sandwich, and in several others situated towards the 54th and 59th degrees of south latitude, the mountains even in the southern summer remain covered with snow quite to the shores of the sea.

This diminution of heat appears to cease all at once be tween the 30th and 40th degrees of latitude; for hot winds arise from the interior of New Holland, whilst the mountains of Van Dieman's Land remain covered with perpetual snow; thus there is felt in these latitudes the most sudden transition from a suffocating heat to a very sensible cold. See, for farther information, respecting the causes of this phenomenon, M. Malte-Brun's System of Geography.

12. Climate, in a geographical sense, is a part of the surface of the earth contained between two small circles parallel to the equator; and of such a breadth, as that the longest day in the parallel nearer the pole, exceeds the longest day in that next the equator, by half an hour, in the torrid and temperate zones; or by one month in the frigid zones.

13. Physical climate comprehends the degree of heat and cold, the drought, the humidity, and the salubrity, which occur in any given region of the earth. The causes of physical climate are nine in number:

1st, The action of the sun upon the atmosphere. 2d, The interior temperature of the globe. Sd, The elevation of the earth above the level of the ocean. 4th, The general inclination of the surface, and its local exposure. 5th, The position of its mountains relatively to the cardinal points. 6th, The neighbourhood of great seas, and their relative situation. 7th, The geological nature of the soil. Sth, The degree of cultivation and population at which a country bas arrived. 9th, The prevalent winds. M. Malte-Brun, Book XVII.

QUESTIONS.

What is the true latitude of a place on the terrestrial globe?

What is the reduced latitude of a place on the surface of the earth?

What is the longitude of a place, and how is it reckoned?

What is the greatest longitude a place can have? What is the declination of a heavenly body, and

how is it reckoned?

What is a zone, and into how many zones is the earth divided ?

What is the situation, and what is the extent of the torrid zone?

Where are the two temperate zones situated, and what is the extent of each?

Where are the two frigid zones situated, and what is the extent of each?

What is a climate in a geographical sense, and what is a physical climate?

CHAPTER. VII.

Of the Natural and Artificial Divisions of Time. 1. Time relatively to us, is the impression which a series of objects leaves upon the memory, and of which we are certain the existence has been successive.

Absolute, true, and mathematical time, of itself, and from its own nature, flows equally without regard to any thing ex-ternal, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year..

2. Mankind have universally agreed to make use of the diurnal and annual motions of the sun, for the purpose of measuring time.

It is proper to observe, that whenever the motion of the sun is spoken of, it is not to be understood in a positive sense, as if he actually removed from one part of space to another, but only as an appearance occasioned by the real motion of the earth in a contrary direction. The pheno mena are exactly the same; and astronomers sometimes, mention one, and sometimes the other, according as they. find it most convenient for their purpose,

3. The interval of time from the sun's centre leaving any meridian to its returning to the same again, is called a true solar day; and is counted twenty-four hours without interruption; that is, in numerical succession from 1 to 24.

This is usually called an astronomical day, because astronomers reckon their day from noon: It is also called a natural day, because it is of the same length in all latitudes. True solar time is that which is shown by a true sun-dial.

4. A mean solar day is the time elapsed from 12 o'clock at noon on any day, to 12 o'clock at noon on the next day, as shown by a perfectly well regulated clock or watch.

The time shown by a well regulated clock, or watch, and a true sun-dial, is never the same but on or about the 15th of April, the 15th of June, the 1st of September, and the 24th of December. The clock, if it goes equally and true, will be faster than the sun from the 24th of December till the 15th of April; from that time till the 15th of June the sun will be faster than the clock; from the 15th of June till 1st of September the clock will be again faster than the sun; and from thence to the 24th of December the sun, will be faster than the clock.

The difference between the true solar noon, as shown by a true sun-dial, and the mean solar noon as shown by an equally going clock, is the greatest about the 3d of November; the time shown by the clock being then 16 minutes and 15.9 second slower than the time shown by the sun-dial.

Though the difference between the true and mean solar noons about the 3d of November, is 16 minutes and a quarter nearly, we are not however to infer that the difference between the mean solar day and true solar day, is equal to the same; for, in fact, they are nearly equal at that time, as may be readily seen from the Nautical Almanac for the present year.

'The difference between mean and apparent time, usually called the equation of time, depends upon two causes, the obliquity of the ecliptic with respect to the equator, and the unequal motion of the earth in an elliptical orbit. The effects of both these causes shall be fully considered in a subse ont part of this work.

5. The civil day is from midnight to midnight again, the first twelve hours are the morning hours, and the last twelve the afternoon hours.

The astronomical day begins at the noon of the civil day; for instance, May 13th, at 4 o'clock in the afternoon, according to the civil account, will be the same as the astronomical account; but supposing it was 4 o'clock in the morning of May 13th, according to the civil account, it would be May 12th, 16 hours by the astronomical way of reckoning.

In civil life, according to Laplace, the day is the interval of time which elapses between the rising and setting of the sun, and is variable according to the different latitudes of places: the night is the time which the sun remains below the horizon, and varies in like manner.

6. The time in which any star appears to re volve from the meridian to the meridian again; or, which amounts to the same thing, the time in which the earth makes one complete revolution on its axis, is called a sidereal day, which is twenty-three hours, fifty-six minutes, four and one-tenth seconds of mean solar time.

A sidereal day is, therefore, less than a mean solar day, by 3 minutes 55.9 seconds. This difference is occasioned by the immense distance of the fixed stars; for the earth's orbit, when compared with this distance, is but a point; and therefore any meridian will revolve from a fixed star to that star again, in exactly the same time as if the earth had only a diurnal motion, and was to remain for ever in the same part of its orbit.

But this is not the case with respect to the sun; for as the earth, at a mean daily motion, advances 59′ 8.2" eastward in its orbit, and that its diurnal motion is also eastward, it is evident that the same meridian can never be brought round from the sun, to the sun again, by one entire revolution of the earth upon its axis, but that it will require as much more of another revolution as is equivalent to the space which the earth has advanced in its orbit during that time. So that three hundred and sixty-six terrestrial revolutions would be exactly equal to three hundred and sixty-five diurnal revolutions, if the equinoctial points were at rest in the heavens.