4 A Synopsis of the principal 



The Sun. . 



The Sun, which is the source of light and heat to our 

 system, is the most considerable of all the heavenly bodies j 

 and governs all the planetary motions. 



Its diameter is 11I*45-JI times the mean diameter of the 

 Earth: whence \X^ volume is 1384472 times greater than 

 thatof the Earth : but itsw«5«is only 33 708G times greater. 

 Whence we conclude that its demihj is -jVxt^j ^"^ about ^ 

 that oFour globe. 



Jt is surrounded by an atmaphere : and it is oftentimes 

 covered with spots. Some of these spots have been ob- 

 served so large as to exceed the Earth 4 or ^ times in mag- 

 niiude. 



The observation of these spots shows that the Sun moves 

 on its «a'J5, which is nearly perpendicular to the ecliptic: 

 and the duration of an entire sidereal rotation of the Sun 

 is about 25^ days. 



Whence we conclude that the Sun is flattened at th? 

 poles. 



The solar equator is inclined 1'^ 30' to the plane of the 

 ecliptic. 



A body, which weighs one pound at the surface of 

 the Earth, would, if removed to the surface of the Sun, 

 weigh '27-933 pounds. And bodies would fall there with 

 a veiotMty of 334'fi5 feet in the first second of time. 



The Sun, together with the planets, moves round the 

 common centre of gravity of the system ; which centre is 

 nearly in the centre of the Sun. 



This motion changes into ep. cycloids the ellipses of thq 

 planets and comets, which revolve round the Sun. 



The Sun appears to have a particular motion, which car-^ 

 ries our system towards the constellation of Hercules. 



The apparent diameter of the Sun, as seen from the Earth, 

 underi'^oes a periodical variation. U is greatest when th^ 

 Earth is in its perihelion; at which time it is 32' 3b", G: 

 and it is least when the Earih is in its aphelion ; at which 

 time it is 3l' 3l'',0. Its mean apparent diameter is therefore 

 32' 3",3. 



His horizontal parallax is 8^". 



The greatest eijiiatwn of his centre is 1° 55' 27'^,7.; which 

 diminishes at the rate of i6",9 in a century. 



The diurnal motion of the Sun from east to west, and 

 h'\'i anJiual qiotion in the ecliptic, are optical deceptions; 

 arisinsf from the real motion of the Earth on its a^^is, and 

 in lis orbit, 



Th€ 



