zon; then that elevation of the pole will be the titude.

EXAMPLES.

In what latitude is the longest day 16 hours? -Anf. 51 degrees.

Find the latitude where the longest day is 12, 3, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 31⁄2 hours.

PROBLEM LII.

To place the Globe in the Situation of the Earth with respect to the Sun, at the Time of the Summer Solstice*.

Rectify the globe 23 deg. north latitude, which is the fun's greateft declination, or diftance from the equator, and conceive the fun to be in the zenith, the globe is then in the fame fituation, with respect to the fun, as the earth is at the time of the fummer folítice: and the following obfervations may be verified by infpection of the globe. 1. All thofe places which lie within the north polar circle, it will be feen, are conftantly above the horizon; to the inhabitants of all these

The word folftice is derived from the Latin words fol, the fun, and to, to ftand, or continue in the fame place, becaufe, when the fun arrives at either of the folftitial points in the heavens, it feems to stand ftill, that is, to make the length of the days neither increase nor decrease fenfibly for about twenty days together, and then he returns towards the other; which happens twice a year, in the fummer and winter. See Art. 12, page 12.

places,

places, therefore, there is continual day. 2. AH thofe places which lie within the South polar circle, are conftantly below the horizon; at thefe places, therefore, there is continual night. 3. If any place be brought under the brafs meridian, and the hour index fet to 12; and if the place be then brought to the eastern fide of the horizon, the hour index will fhew the time' of fun-rifing and fun-fetting at that place; whence the length of the folftitial, or longest day, may eafily be found. See the note to Problem 12, p. 41. and the N. B to Problem 17, P. 48.

To place the Globe in the Situation of the Earth at the Time of the Winter Solftice.

Rectify the globe to 23 deg. South latitude, which is the fun's declination on the folftitial day; the globe is now in the fame fituation as the earth is, with refpect to the fun, at the winter folftice. The obfervations that arife from this view of the

globe are as follow: 1. It will be apparent that the whole fpace within the South polar circle is in the fun's light, and enjoys continual day. 2. The whole fpace within the North polar circle is in the fhade, and has continual night. 3. If any place be brought to the meridian, as in the lait problem, the horary index will fhew that the day is equal to what the length of the night was in that place, at the fummer folftice; and that the hour of fun-fetting is the fame as that of fun-rifing at the fummer folftice; and, on the contrary, the hour of fun-fetting at the winter, is the fame as that of fun-rifing at the fummer folftice.

It

It may be proper here to remark, that all places n the earth do equally enjoy the benefit of the in in respect of time, and are equally deprived of . For, at the Poles the day and night are alterately half a year each; at the Equator the day always 12 hours, and the night the fame; and all intermediate places (thofe within the polar ircles excepted, where the days are from 24 ours to 6 months in length, according to the titude, and the nights the fame, at the oppofite afon) the days are always as much longer than 2 hours in fummer, as they are fhorter in winer hence it is clear, that in the whole course of The year the fun is feen at all places an equal Space f time.

OF

OF THE

CELESTIAL GLOBE.

WE

E have already obferved *, that the cele tial globe is a reprefentation of the heavens On its furface are placed all the ftars of the fir and fecond magnitude, and the most noted of the reft which are vifible. The ftars are disposed inte conftellations †, under the forms of fuch animals, or other figures, as are delineated on this globe; which were invented by the ancient aftronomers and poets, and are ftill retained for the fake of distinction, and to avoid confufion in comparing the ancient and modern observations. The ftars

See page 4.

in

+ The word conftellation, in aftronomy, means an affemblage or fyftem of feveral ftars; and this group is by fome called an afterifi.

Some, it has been remarked, out of vain zeal, rather than any love for the fcience, have been induced to alter either the figures of the conftellations, or at least their names. Thus, Venerable Bede," instead of the prophane names and figures of the twelve conftellations of the Zodiac, fubilituted thofe of the twelve Apoitles; whofe example being followed by Julius Schillerius, in 162-, he completed the reformation, and gave fcripture names to all the conitellauces in the heavens. Weigelius, profeffor of mathematics in the

famous

In each conftellation are marked with Greek leters *, and some remarkable ones are called by particular names. Thofe ftars which are not comprehended in any constellation, are called unformed tars; and fome which have a cloudy appearance, are denominated nebula. Thofe ftars which cannot be seen without the affiftance of a telescope, are called telescopic stars.

The heavenly bodies now under confideration are called fixed ftars, because they always maintain the fame pofition or relative distance from each other; their apparent diurnal motion being caused folely by the earth's turning on its axis. They are easily distinguishable from the planets + by an inferiority of brilliancy and light, and by an uniform exhibition of the appearance termed fcintillation, or twinkling. They are fuppofed to famous Univerfity of Jena, in Upper Saxony, made a new order of constellations; converting the firmament into a cælum beraldicum, and introducing the arms of all the princes of Europe, by way of conftellations. But the more learned among the aftronomers never approved of innovations, as ferving no purpose but to introduce confufion into astronomy.

* John Bayer, of Augsburgh, about the year 1603, introduced the custom of marking the ftars in each conftellation, by the letters of the Greek and Roman Alphabets. This he borrowed from the Jews; who, to avoid the figures of animals, forbidden by their law, had used the letters of their alphabet.

The first letter of the Greek alphabet is generally affixed to the brightest star in each constellation; the fecond letter to the next, and fo on. If there are more ftars in the conftellation than letters in the Greek alphabet, the remainder are marked with the letters of the Roman alphabet, or in Italics.

The first perfon who numbered the ftars and reduced them to order was Hipparchus. See page 23.

+ See Planets, Index,

be