THE LEVELLING POWER OF RAIN. 385 



soil of India and delivers into the sea t \vice as much solid 

 substance as is contained in the great pyramid of Egypt 

 " The Irrawaddy," says Sir J. Herschel, " sweeps off from 

 Burmah 62 cubit feet of earth in every second of time on 

 an average, and there are 86,400 seconds in every day, and 

 365 days in every year ; and so on for other rivers. Nor is 

 there any reason to fear or hope that the rains will cease, 

 and this destructive process come to an end. For though 

 the quantity of water on the surface of the earth is pro- 

 bably undergoing a slow process of diminution, small 

 portions of it year by year taking their place as waters under 

 the earth,* yet these processes are far too slow to appreciably 

 affect the supply of water till a far longer period has elapsed 

 than that during which (in all probability) life can continue 

 upon the earth. 



When we consider the force really represented by the 

 downfall of rain, we need . not greatly wfender that the 



Those whose custom it is to regard all theorizing respecting the 

 circumstances revealed by observation as unscientific, may read with 

 profit an extremely speculative passage in Newton's Printipia relating 

 to the probable drying up of the earth in future ages. " As the seas," 

 he says, "are absolutely necessary to the constitution of our earth, 

 that from them the sun, by its heat, may exhale a sufficient quantity of 

 vapours, which, being gathered together into clouds, may drop down in 

 rain, for watering of the earth, and for the production and nourishment 

 of vegetables ; or being condensed with cold on the tops of mountains 

 (as some philosophers with reason judge), may run down in springs 

 and rivers ; so for the conservation of the seas and fluids of the planets, 

 comets seem to be required, that, from their exhalations and vapours 

 condensed, the wastes of the planetary fluids spent upon vegetation 

 and putrefaction, and converted into dry earth, may be ultimately 

 supplied and made up ; for all vegetables entirely derive their growths 

 from fluids, and afterwards, in grea measure, are turned into dry earth 

 by putrefaction ; and a sort of slime is always found to settle at the 

 bottom of putrefied fluids ; and hence it is that the bulk of the solid 

 earth is continually increased ; and the fluids, if they are not supplied 

 from without, must be in a continual decrease, and quite fail at last 

 I suspect, moreover, that it is chiefly from the comets that spirit comes 

 which is indeed the smallest but the most subtle and useful part of our 

 air, and so much required to sustain the life of all things with us." 



2 C 



