ASTRONOMY. 



same meridian, observing at the same in- 

 stant the meridian altitude of the centre 

 of the sun, and his distance from the same 

 pole. The difference of the two distan- 

 ces observed will be the angle under 

 which the line which separates the obser- 

 vers will be seen from the centre of the 

 sun. The position of the observers gives 

 this line in parts of the earth's radius. 

 Hence it is easy to determine, by obser- 

 vation, the angle at which the semidi- 

 ameter of the earth would be seen from 

 the centre of the sun. This angle is the 

 sun's parallax. But it is too small to be 

 determined with precision by that me- 

 thod. We can only conclude from it, 

 that the sun's distance from the earth is 

 at least equal to 10,000 diameters of the 

 earth. Other methods have been disco- 

 vered for finding the parallax with much 

 greater precision. It amounts very near- 

 ly to 8".8 : hence it follows, that the dis- 

 tance of the sun from the earth amounts to 

 at least 23.405 semidiameters of the earth. 

 The sun was long considered, from its 

 constant emanation of heat and light, as 

 an immense globe of fire. When viewed 

 through a telescope, several dark spots 

 are visible on its surface, which are of 

 various sizes and durations. From the 

 motion of these spots, the sun has, be en 

 found to move round its axis, and its axis 

 is found to be inclined to the ecliptic. 

 Various opinions have been formed re- 

 specting these spots ; they have been con- 

 sidered as opaque islands in the liquid 

 igneous matter, and by some as pits or 

 cavities in the body of the sun. In 1788, 

 Mr. King published a Dissertation on the 

 Sun, in which he advanced, that the real 

 body of the sun is less than its apparent 

 diameter ; that we never discern the real 

 body of the sun itself, except when we 

 behold its spots ; that the sun is inhabit- 

 ed as well as our earth, and is not ne- 

 cessarily subject to burning heat ; and 

 that there is in reality no violent element- 

 ary heat existing in the rays of the sun 

 themselves essentially, but that they pro- 

 duce heat only when they come into con- 

 tact with the planetary bodies. Several 

 years after this, Mr. Herschel published 

 his theory of the nature of the sun, which 

 is briefly as follows : he considers the sun 

 as a most magnificent habitable globe, 

 surrounded by a double set of clouds. 

 Those which are nearest its opaque body 

 are less bright, and more closely connect- 

 ed together, than those of the upper stra- 

 tum, which form the luminous apparent 

 globe we behold. This luminous exter- 

 nal matter is of a phosphoric nature, hav- 



ing several accidental openings in it) 

 through which we see the sun's body, or 

 the more opaque clouds beneath. These 

 openings form the spots that we see. 



Mercury. This planet being the nearest 

 to the sun, and the least in magnitude, is 

 very seldom visible. It never appears more 

 than a few degrees from the sun's disc, 

 and is generally lost in the splendour of 

 the solar beams. On this account astro- 

 nomers have had few opportunities of 

 making accurate observations upon it ; 

 no spotshave been, observed upon it, con- 

 sequently the time of its rotation on its 

 axis is not known. Being an inferior pla- 

 net, it consequently must show phases 

 like the moon ; and it never appears quite 

 full to us. It is seen sometimes passing 

 over the sun's disc, which is called its 

 transit. 



Venus is the brightest and largest, to 

 appearance, of all the planets, and is dis- 

 tinguished from the rest by her superio- 

 rity of lustre. It is generally called the 

 morning or evening star, according as it 

 precedes or follows the apparent course 

 of the sun. Some have thought that they 

 could discover spots upon its disc, but 

 Herschel has not been able to see them ; 

 consequently, the time of rotation round 

 its axis is not decidedly known. Venus al- 

 so appears with phases, and transits some- 

 times take place, which are of very great 

 importance in astronomy. 



The Earth, which we inhabit, is, as has 

 been proved, a globular body ; it is not, 

 however, a perfect sphere, but a spheroid, 

 having its equatorial diameter longer than 

 the polar diameter, or axis. It is conse- 

 quently flattest at the poles, and more 

 protuberant at the equator. The diame- 

 ter at the equator is 7893 English miles ; 

 that at the pole is 7928 miles. The sur- 

 face of the earth is much diversified with 

 mountains and vallies, land and water. 

 The highest mountains in it are the An- 

 des, in South America, some of which are 

 about four miles in perpendicular altitude. 

 About two-thirds of the globe is covered 

 with water. In consequence of the earth's 

 being a globe, people standing upon op- 

 posite sides of it must have their feet to 

 wards each other. When in this situation, 

 they are called antipodes to each other. 

 Hence it appears that there is no real up 

 or down ; for what is up to one country is 

 down to another. It must seem strange 

 to those who are ignorant of the shape of 

 the earth, to suppose, that if we could 

 bore a hole downwards, deep enough, 

 we should come to the other side of the 

 world, where we should find a surface 



