RELATION OF EAETH TO SUN AND MOON 



11 



of the weight and the pull of the band, was to make the 

 path of the weight lie between the two. In this case the 



forces at every instant 

 almost balanced each 

 other, and the path was 

 nearly a circle. It is 

 the force of gravitation 

 acting against the iner- 

 tia, or the centrifugal 



PUSH 



THREE FORCES IN PLAY. 



Fig. 5. 



force, of the heavenly bodies which holds them in their 

 orbits. 



4. Relation of the Earth to Sun and Moon. Not only do 

 all the planets revolve around the sun, but certain of these 

 themselves have other smaller bodies revolving around 

 them. We call such small bodies satellites or moons. The 

 earth has one of these satellites and Saturn has the greatest 

 number of all, ten, one having been discovered as late as 

 1905. Our own moon has a diameter of about 2000 miles and 

 a weight of about -fa that of the eartfy. Its average distance 

 from the earth is about 240,000 miles. Compared with the 

 distance of the other heavenly bodies it is indeed very near. 



The sun, although a near neighbor as compared with the 

 rest of the stellar community, is at an average distance of 

 about 93,000,000 miles. It is so big that if it were hollow 



