WEIGHING THE WORLDS 



period. Another computation will show that in the 

 circle thus constituting the earth's path, an arc 

 eighteen and a half miles in length departs from a 

 straight line only an infinitesimal amount; in short, 

 by just about one-ninth of an inch. In other words, 

 the earth in compassing a distance of eighteen and 

 a half miles falls toward the sun, under the influence 

 of gravitation, by one-ninth of an inch. 



Now it is familiar knowledge that an object near 

 the earth's surface falls toward the earth's centre six- 

 teen feet in the first second. It follows that the force 

 of gravitation as exerted by the earth on objects at 

 its circumference is greater than the force of gravi- 

 tation exerted by the sun on matter at the earth's dis- 

 tance in the ratio of sixteen feet to one-ninth of an 

 inch. But objects at the earth's centre are only 3964 

 miles from the earth's centre of gravity, whereas the 

 earth is 92,900,000 miles from the sun's centre of 

 gravity; and as the force of gravitation decreases with 

 the square of the distance, the ratio that expresses 

 the relation between the actual gravitation of the 

 earth and that of the sun is the ratio between the 

 square of 3964 miles and the square of 92,900,000 

 miles. 



The arithmetical computation being made it ap- 

 pears that the actual mass of the sun is 332,000 times 

 that of the earth. In other words, could the sun be 

 placed on one scale of a gigantic balance, 332,000 

 globes such as ours must be placed in the other scale 

 to offset his weight. Even as colossal a weight as 

 this, however, does not come up to the expectations 

 based simply on the sun's bulk; for it appears that 



7.1 



