from a light-house, but do not see the lantern. The most powerful telescope fails to reveal the faintest trace of a disk. At the present time the nearest star to the earth is Alpha, in the Constellation of Centaur. It is estimated to be over 20,000,000,000,000 miles distant; this means that it is not inside this distance, but how much farther away it may be is unknown. It takes the light from it 31⁄2 years to reach us.

The fixed stars, so called, are flying through space at an amazing rate; for instance, Arcturus, with a speed of 200,000 miles per hour, requires 3 centuries to traverse as much of the starry vault as equals the moon's

apparent diameter. This will give some idea of heavenly distances. The fact that stars shine by their own light proves that they are suns like our own, which is quite a small star, sweeping the heavens at the rate of 150,000,000 miles per year.

Number.-The stars seem to us innumerable, but in fact the entire number visible is but 6000, while but few people can discern more than 4000.

Magnitude. The classification of the stars is made from their comparative brilliance, as nothing is known of their size. They are arranged in 20 classes or magnitudes. There are about 20 stars of the first magnitude, 65 of the second, 200 of the third, 1100 of the fifth, 3200 of the sixth, 13,000 of the seventh, 40,000 of the eighth, and 142,000 of the ninth. But

few persons can see stars of less magnitude than the fifth or sixth. The relative brightness may be due to size, distance, or intrinsic brightness. Many of the stars were named at an early date, as Sirius and Arcturus. The chief stars of each constellation are called after the letters of the Greek alphabet, according to their relative brightness.

Constellations.-From the earliest times the stars have been arranged in groups, to more readily study them, and took on fanciful names from their fancied resemblance to natural objects, mythology being largely drawn upon for this purpose.

The best known constellation is the Great Bear or Dipper. The next

Ursa Minor, or Little Bear, or Little Dipper, containing the North Star. The Bible refers to Orion and the Pleiades.

The signs of the Zodiac are 12 constellations, arranged as follows: Aries, the ram, so named because it rose with the sun in the spring. Then came Taurus, the bull, and Gemini, the Twins. At the summer solstice the sun appeared to stop, and crab-like go backward, hence Cancer, the Crab. When Leo, the Lion, appears, the streamlets are dry. Virgo comes next, when the virgin gleans the summer harvest. When the days and nights are equal, at the Autumnal Equinox, Libra, the balance, reigns. When the summer days are gone, the Scorpion arrives in the heavens. When the hunters are abroad, Sagittarius, the archer, bends his bow in the sky. At the winter solstice, December 21st, Capricornus, the goat, climbs the heavenly arch, and finds the sun ascending the sky on his return north. The rainy season, January, has Aquarius, the Water-bearer. Pisces, the fishes, complete the round of the months.

Although all the stars look like a single luminary, the telescope says that 10,000 of them are double; i. e., the ray of light is the blended emanation of two suns. The North Star consists of two stars 18° away from each other. The Dog Star (Sirius) has two 7 distant from the other.

Colored Stars.-The stars are different colors. Sirius is white, some are red, while others are yellow, blue, and green.

The Variable Stars have periodical changes of brilliancy, variously explained. Some stars suddenly appear with great brilliance, others gradually fade away, giving rise to what are called New Stars and Lost Stars.

The Nebulæ are faint misty appearances like an illuminated cloud. A few can be seen with the naked eye, but the telescope makes thousands visible. It is believed that these are the beginnings of stars, or sun germs. They are variously shaped, ring-like, spiral, oval, etc. One looks like a dumb-bell, another like the wings of a bird, and yet another has the appearance of a crab.

Astronomical study is now occupied in determining the constitution of the stars, and by the Spectrum Analysis much is being determined that seems incredible. The rays of light are passed through a prism, and by refraction compared with those made by metals that are heated to incandescence.

Time. The time of day is measured by the interval required by the earth to rotate on its axis, the time certain stars rise, as well as the sun, the latter varying more than the former, it being necessary to add one day every four years to even things up.

Parallax is the difference in direction of an object seen from two dif ferent places; for instance, place your finger before you in front of a window, look at it with the left eye only and it will seem to be at one point on the window. Look at it now with the right eye only and it will be located apparently somewhere else on the window. The difference in the position of your finger as seen from your two eyes separately is its parallax. Aberration of Light is the apparent change of position of heavenly bodies due to the refraction of light.

TIME, TIDES AND THE WEATHER.

TIME.

Astronomers make use of several different kinds of time; mean solar time; true or ap parent time, and sidereal time.

Solar Time. Solar time is that used for all the ordinary purposes of life, and is meas ured by the daily motion of the sun. A solar day is the interval of time between two successive transits of the sun over the same meridian, and the hour angle of the sun is called solar time.

This is the most natural and direct measure of time. But the intervals between the successive returns of the sun to the same meridian are not exactly equal, owing to the varying motion of the earth round the sun, and to the obliquity of the ecliptic. The intervals between the sun's transits over the meridian being unequal, it is impossible to regu. late a time-piece so that it shall follow the sun.

To avoid the irregularity which would arise from using the true sun as the measure of time, a fictitious sun, called a mean sun, is supposed to move in the equator with a uni form velocity. This mean sun is supposed to keep, on the average, as near the real sun as is consistent with perfect uniformity of motion; it is sometimes in advance of it, and sometimes behind it, the greatest difference being about 16 minutes.

Mean solar time, which is perfectly equable in its increase, is measured by the motion of this mean sun.

The clocks in ordinary use, and the chronometers used by navigators, are regulated to mean solar time. Mean solar time is generally called mean time simply.

True or apparent solar time is measured by the motion of the real sun. The difference between apparent and mean time is called the equation of time; by means of it we change apparent to mean time, or the reverse.

Sidereal Time. Sidereal time is measured by the daily motion of the stars; or, as it is used by astronomers, by the daily motion of that point in the equator from which the true right ascensions of the stars are counted. This point is the vernal equinox, and its hour angle is called sidereal time. Clocks regulated to sidereal time are called sidereal clocks.

A Sidereal Day is the interval of time between the transit of the vernal equinox over any meridian and its next succeeding return to the same meridian. It is about 3 m. 56 s. shorter than the mean solar day; 365 solar days, or a year, being divided into 366 sidereal days. It is divided into 24 hours. The sidereal hours are counted from o to 24, commencing with the passage of the vernal equinox over the upper meridian, and ending with its return to the same meridian. About March 21 of each year, the sidereal clock agrees with the mean time or ordinary clock, and it gains on it about 3 m. 56 s. per day, so that at the end of a year it will have gained an entire day, and will again agree with it.

The Civil Day commences at midnight, and comprises twenty-four hours from one midnight to the next following, The hours are counted from o to 12 from midnight to noon, after which they are again reckoned from o to 12 from noon to midnight. Thus the day is divided into two periods of 12 hours each, the first of which is marked A. M., the last is marked P. M.

The Astronomical Day commences at noon on the civil day of the same date. It also comprises twenty-four hours; but they are reckoned from o to 24 hours, and from the noon of one day to that of the next following. The astronomical as well as the civil time may be either apparent or mean, according as it is reckoned from apparent noon or from mean noon. The civil day begins twelve hours before the astronomical day; therefore, the first period of the civil day answers to the last part of the preceding astronomical day, and the last period of the civil day corresponds to the first part of the same astronomical day. The rule then for the transformation of civil time into astronomical time is this: if the civil time is marked A. M. take one from the day and add twelve to the hours, and the result is the required astronomical time; if the civil time is marked P. M., take away the designation P. M. and the astronomical time is obtained without change.

To change astronomical to civil time, we simply write P. M. after it, if it is less than twelve hours. If greater than twelve hours, we subtract twelve hours from it, add one to the days, and write A. M.

If the longitude from Greenwich be expressed in time, and when west added to the local time, or when east subtracted from the local time, the result is the corresponding

Greenwich time. If the local mean time is used, the result is the Greenwich mean time. The rule is the same whether we use mean or sidereal time.

For general convenience, the time changing continually during a passage, apparent time is kept on board ship at sea. This fact must be remembered, if looking out for the meridian passage of stars to determine latitude.

Lunar Day. The average duration of a lunar day, or the interval that elapses between two successive transits of the moon over the meridian of the same place, is 24 h. 54 m.; the average period of the moon's revolution round the earth is 27 d. 7 h. 43 m. 11.5 s. ; while the interval between new moon and new moon is 29 d. 12 h. 44 m. 2.9 s.

At any time of the year, add 12 hours to the time of the sun's setting, and from the sum subtract the time of rising, for the length of the day. Subtract the time of setting from 12 hours, and to the remainder add the time of rising next morning, for the length of the night. These rules are equally true for apparent time.

At Berlin and London the longest day has 161⁄2 hours; at Stockholm and Upsal, 16: at Hamburg, Dantzic, and Stettin, 17, and the shortest 7; at St. Petersburg and Tobolsk the longest has 19, and the shortest 5 hours; at Bornea, in Finland, the longest day has 21%, and the shortest 2. At Wanderbus, in Norway, the day lasts from the 21st of May to the 22d of July, without interruption; and at Spitzbergen the longest day is 3%1⁄2 months.

Year. The earth completes her revolution round the sun in 365 d. 6 h. 9 m. 9.6 s., mean solar time, or in 366 d. 6 h. 9 m. 9.6 s. reckoned in sidereal time. This is called the sidereal year. But the year in which mankind in general are most interested, is the tropical year of 365 d. 5 h. 48 min. 49.7 s.

This year, on which the return of the seasons depends, is the interval between two suc. cessive arrivals of the sun at the vernal equinox, or first point of Aries, and differs from the sidereal year by reason of the motion of the equinoctial points, known as the precession of the equinoxes.

The tropical year is a compound phenomenon, depending chiefly and directly on the annual revolution of the earth round the sun, but subordinately and indirectly on its rotation round its own axis. The Gregorian Calendar, now generally used among civilized nations, depends upon this tropical year, and may be thus briefly described:

Every year whose number is not divisible by 4 without a remainder consists of 365 days; every year which is divisible by 4, but is not divisible by 100, of 366 days; every year divisible by 100, but not by 400, consists again of 365; and every year divisible by 400, consists of 366 days For example:

1873, not being divisible by 4, consists of 365 days.

1876, being divisible by 4, but not by 100, consists of 366 days.

1800 and 1900, being divisible by 100, but not divisible by 400, consist of 365 days each. 2000, being divisible by 400, consists of 366 days.

The error of the Gregorian Calendar amounts to only 0.944 days in 4,000 years.

Scale of units-60, 60, 24, 365..

The tropical (or solar year) and the sidereal years are the same, and the tropical is only