HOUR-ARCS OF A VERTICAL DIAL, ETC.

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place of the shadow at 1 P.M., intersects at an angular distance from the south point of very nearly 9°,-the second, or shadow's place at II, intersects at 1810, &c. &c.; the intersections between the south and west points (and which are the places of the shadow at XI, X, &c.), being at the same angular distances.

Ex. 2. Furnish the remaining hour-arcs on the abovementioned dial.

Ex. 3. What are the angular distances at which I must draw the lines on a dial intended to be fixed up against the south wall of a church in London ?

Ex. 4. Find the hour-arcs of a vertical dial, facing the south, in Lisbon, and state where this might be used as a horizontal dial (N, p. 385).

Ex. 5. What must be the hour-arcs on a vertical dial, facing the north, placed against a wall in the middle of New Zealand, lat. 381° south?

Ex. 6. Suppose vertical dials facing the north to be required for parts of Chili and New Zealand, in lat. 3510 S., -from which north part of the world might they be supplied without the trouble of manufacturing new ones?

Ex. 7. With the inhabitants of what remarkable places might Edinburgh exchange horizontal dials for vertical ones ?

Ex. 8. Having graduated 24 hours on the whole circumference of a disk of card-board, on both sides, and set it horizontally, I have also inserted a straight pencil half-way through its centre, with care to keep it perpendicular to this plane or disk :—

If I now raise the south point of this plane to the complement of my latitude, so as to direct it to the equinoctial in the heavens, to what two points in the heavens will the ends of the pencil be directed-with what great circle of the earth will the disk be parallel-for what two places diametrically opposite to each other will the surfaces of the card be horizontal dials-why will such a disk shew me my solar time-and on which side of it will shadows be cast during my winter hours?

PROBLEM Z.

CELESTIAL GLOBE.

To map down a group of constellations, having a certain star given as central.

RULE.-1. Bring the given star to the brass meridian, and elevate the pole to its declination :-attach the quadrant of altitude over the star, and (by Prob. X. p. 87) make out a list of the stars around it with their degrees of distance from this central star, and with the several bearings they have from it whilst it is thus in the zenith.

2. Having described a circle of convenient size on a piece of card-board or stiff paper, and drawn diameters at right angles, mark the uppermost point N.- the undermost S.the right-hand point W.-and the left-hand point E.;the degrees of each quadrant being set off from N. or S. toward W. or E. by a protractor.*

**

3. At the centre of this circle mark the Greek letter and number expressing the magnitude of the star used for the central one of the group; and then, by means of the graduated edge of the quadrant of altitude, set off pencil dots at the degrees of distance and several bearings registered in the list just made; marking each of such dots (as soon as made) with the Greek letter and magnitude of the star it represents.

4. If the places of these dots be now carefully pierced with pins of different thicknesses, the card or paper will be of considerable assistance in tracing the constellations

* When we have not a protractor at hand, the degrees of a circumference may be set off from the equator of the globe, if we draw it with the semi-diameter of the globe; or, if this be too large for the paper, each half degree of the globe will be a degree on a circumference drawn with half its semi-diameter :-thus, for instance, if we draw a circle with the compasses open three inches, we may use for degrees the half-degrees of a twelve-inch globe.

MAPPING CONSTELLATIONS.

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in the heavens ; * especially if the outlines of the figures to which the stars of the group belong, be lightly traced with a pen dipped in oil or varnish, to render them partially transparent.

Ex. 1. Taking y of Ursa Major as a centre, map down the stars in Ursa Major and Ursa Minor.†

Ex. 2. Taking ♪ of Orion as the central star, map down the stars in Orion,—Lepus,—head and horns of Taurus,Canis Major,-Canis Minor,-and heads of Gemini.

Ex. 3. Taking 8 of Cygnus as central, draw, and prick out, the group containing Cygnus, Lyra, Aquila, and Delphinus.

* The constellations beyond the bounds of the card, and even those below the horizon, may be imagined and readily pointed towards by the aid of the" Rhymes on the Constellations," given in the Appendix. The author is aware that such a 'mapping' will be distorted; but the advantage will, nevertheless, be considerable.

ASTROLOGY.

P THE terms astronomy (αστρονομια) and astrology (αστρολογία) were synonymous amongst the Greeks, and Cicero uses the word astrologia in a similar manner.

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But judicial astrology," a pretended science, was very generally received among the nations of antiquity (except the Greeks), and was also much cultivated in Europe during the middle ages. The basis of this science was the supposition that the heavenly bodies affected the destinies of mankind.

A knowledge of the terms and principles of this pretended art is desirable as furnishing a key to expressions made use of by several authors.

The apparent hemisphere of the sky was divided into six portions, by imaginary lines, like the meridional semicircles. of the common globe, but originating in the north point of the horizon of any place and terminating in its southern point. The hemisphere below, and invisible, being divided in similar manner, the twelve divisions were called "houses of heaven." The principal points attended to in each 'house' were the part of the Zodiac which occupied it at any instant as the heavens revolved from east to west through these twelve stationary' houses,' and—the place of any planet which, from its position in the Zodiac, might happen to be in a certain house' at that certain time.

R.These houses 'had different 'powers.' The strongest was the first, which contained the part of the heavens about to rise; this was called the ascendant;' and the point of the ecliptic which was just rising was called the 'horoscope.

The twelfth was the house' just above and along the eastern horizon; and the tenth, which was that from which

the heavenly bodies were just culminating, was the next or second in power.'

S" Each house' had one of the planetary bodies as its ' lord,' who was stronger in his own house than any other, as was fit;—and, of two planets equally strong' in other respects, he who was in the stronger house was the stronger.

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*

*

*

*

In the fifteenth century Stoffler * foretold a universal deluge which should take place in 1524, in consequence of three planets being then in conjunction in a watery sign. All Europe was in consternation, and those who could find the means built boats in readiness. A doctor of Toulouse is said to have made an ark for himself and his friends.' Penny Cyclopædia.

[In the same century, Pope Calixtus III. directed prayers and anathemas against a comet, which had either assisted or predicted the success of the Turks against the Christians.]

T Astrologers have disregarded the very important circumstance of the Precession of the Equinoxes (see p. 354), although Aries, Taurus, &c., are now, in consequence of this, a whole sign in advance of their former situations in the ecliptic!

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A number of infamous characters, sometime after their death, are made gods and goddesses:-In a course of years their names (Mercury, Venus, &c.) are arbitrarily imposed on the planets which have existed from the beginning of the world. Then the various attributes, such as stupidity, moroseness, deceit, wantonness, cruelty, and the like, for which these gentry were celebrated, are supposed to be transmitted with their names, and a small portion of some sort of goodness, to the different planets where they then reside; but whether upon them or in them does not exactly appear.

Then these large dark insensible bodies, with their fine tempers, as they continue their mystic dance round the

*A German mathematician.