SOMh OF THE IVASTES OF NATURE. 415 



surface of the earth and see how long it will take for the progeny of a single plant 

 to completely cover it with vegetation. The land portion of the earth's surface 

 contains about 47,000,000 square miles. Reduced, this gives us 1,310,284,800,- 

 000,000 square feet. Now let us take a plant that will average 500 seeds a year, 

 which is a very low estimate, as many produce several thousands of seeds annual- 

 ly. Now suppose every seed should be preserved and grown for seven years 

 and the product for the last year would be 7.812,500,000,000,000,000 plants, 

 which would be equal to 5,962 for every square foot of land on the earth's sur- 

 face. But if we estimate the annual increase at only loo-fold, then in nine years 

 the product would give 763 plants to each square foot of surface, which, even at . 

 this low estimate, will be seen to be many times as much as could possibly grow 

 on the given space ; and this makes no allowance for deserts or barren mountains, 

 which occupy no inconsiderable portion of the earth's surface. This proves that 

 a very large proportion of the annual production of seeds perish without having 

 served any apparently useful purpose in the economy of nature. 



In the employment of the forces of nature there seems to be a vast expendi- 

 ture of energy the utility of which we are unable to discover. A forcible illustra- 

 tion of this waste of energy is found in the force that is constantly employed in 

 lifting the waters of the earth to the aerial regions where they are formed into- 

 clouds and afterward precipitated in rain, hail and snow. The amount of water 

 thus lifted up by evaporation to an average height of three and one-half miles is 

 equal to 2,000,000,000 tons per minute. This would be equal to the continued 

 exercise of the combined strength of more than 2,239,000,000,000 horses. Of 

 the vast energy with which this force operates we have an example in some por- 

 tions of the Indian Ocean, particularly the Bay of Bengal, where at times the 

 evaporation is as much as from twenty to thirty inches in depth over the whole 

 surface in twenty-four hours. Not only is this vast volume of water e'evated to 

 this great height but it is conveyed to great distances, frequendy hundreds of 

 miles, where it is poured down in rain or snow. It should be remembered that 

 when this vast amount of vapor has been elevated to this great altitude it con- 

 tains a latent energy equal to that which has been exerted in lifting it to its pres- 

 ent position. And in returning to the level of the ocean, as it all does eventual- 

 ly, it gives out this latent energy. Every drop of water that falls gives up in its 

 descent an amount of energy just equivalent to that which was expended in lifting 

 it up to its highest altitude. Every stream that flows is evolving this energy thus 

 stored up in its waters. 



This evolution of energy is constantly going on before our eyes in the va- 

 rious rivers that flow by us on their way to their ocean home. 



The amount of power that is continually going to waste in the rivers of the 

 Earth is entirely beyond our calculation. Take a single instance — that of the 

 Falls of Niagara, 100,000,000 tons of water plunge over that precipice every 

 hour. Here we have a loss of not less than 56,000 horse-power every minute;, 

 about three and a half times the amount of power developed by burning all the 

 coal dug from all the mines in the world. But this great cataract represents. 



