Dr Seller on the Nutrition of Plants. 67 



—Air, Water, Earth, and Fire, are in truth the elements of 

 the organic world; for their fire represents that warmth, 

 the absence of which extinguishes all organic life. 



A brief notice of the mode in which the numerical results made use of 

 have been brought out may be satisfactory, and will shew that no ex- 

 aggeration has been practised to the prejudice of the opinion that the 

 food of plants is organic substance. 



The area of the earth's surface is roundly estimated in square miles, 

 by multiplying the circumference into the diameter. 



24,000 X 8000 = 192,000,000, area of the earth In square miles. 



^^ ^r.r. f one-fifth part of the earth's 

 192,000,000 =38,400,000, | ,^rface in square mUes. 

 5 

 The number of square feet in a square mile is 27,878,400 ; whence 

 38,400,000 X 27,878,400 = 1,060,520,560,000,000, the number of 

 cubic feet of soil, a foot deep, in the surface of one-fifth part of the area 

 of the earth. 



A cubic foot of water weighs 1000 ounces avoirdupois ; call soil twice 

 the density of water, which is near its density ; then a cubic foot of soil 

 weighs 2000 ounces, or 12'5 pounds : 



125 X 1,060,520,560,000,000 = 132,564,071,000,000,000, 

 which number represents the quantity of soil in avoirdupois pounds con- 

 tained in one-fifth part of the earth's surface. 



The same reduced to tons is 59,180,388,839,285. 

 Take ten per cent, of this quantity as organic matter, 

 5,918,038,883,928. 



Take three-fifths of the organic matter as carbon, 



3,550,823,320,352 ; or there is something more 

 than three billions and a half of carbon in the soil of one-fifth part of 

 the earth's surface. 



If a thousand millions of men consume daily five ounces of carbon 

 each in respiration, they consume in a year 50,922,420 tons of carbon. 

 A horse, according to Boussingault, throws oiF, in carbonic acid, 6-07 

 pounds of carbon, or nearly a ton in a year (-988 ton). 



The horses of Great Britain, on a moderate calculation, are estimated 

 at a million and a half ;* and the inhabitants of Great Britain are les3 

 than a fiftieth part of the human race : say, then, there are fifty times 

 as many horses in the world as in Great Britain, and horses alone will 

 be found to consume every year nearly 75,000,000 of tons of the carbon 

 of organic matter. 



An ox or cow converts nearly four and a half pounds of carbon daily 

 into carbonic acid. Tliere are about three millions and a quarter of 

 cattle in Great Britain ;t or the cattle of Great Britain must consume 



* Macculloch's Btatisticul Account of the British Empire, vol. i. page 284. 

 t lb. page 490, 



