GRAVITATION OF DISTANCE. 107 



vent them from upsetting by the action of the 

 wind on their sails ; and coaches that have a box 

 below, for heavy luggage, are much safer than 

 those that carry a much smaller weight of luggage 

 on the top. 



The gravitation of distance, or of the position which 

 one body has with regard to another, depends, like 

 specific gravity, on two elements, the absolute 

 weight of the body, and the distance ; and it varies 

 with every change in either of these. It is inversely 

 as the square of the distance, and directly as the 

 absolute gravity or quantity of matter. But the 

 gravitation of distance is not affected by the spe- 

 cific gravity ; for if it were not that the air resists 

 the one more than it resists the other, because there 

 is more weight of air opposed to the same weight 

 of it, a cobweb would fall as fast and as straight 

 from the top of St. Paul's, or any other height, 

 as a mill-stone. 



But though the place of no substance can be 

 even in the least changed) without a change in 

 the gravitation of distance, yet the alterations 

 produced by small changes at long distances are 

 very small. The distance of the mean surface of 

 the earth from its centre is about four thousand 

 miles, and the highest mountain known, is less 

 than five miles more, so that the weight of an or- 

 dinary man would not be half a pound less if he 

 were on the top of the mountain than if he were 

 on the sea- shore. Substances that have elasti- 

 city or spring in them, so that they are affected by 

 pressure, show even amuchless elevation than that. 

 The air is altogether a spring, pressed down by 

 its own weight, and it shows the changes of 

 height very nicely. Water boils with less heat 



