90 PROCEEDINGS OF THE ACADEMY OF [1892. 



It is even probable that the efiective power obtainable from the 

 gravitation of water, is not so great as is often assigned it, even in 

 the most favorable climates. The area of Pennsylvania is 45,000 

 square miles, or 28,800,000 acres, and the exti'emes of precipitation 

 on its eastern and western parts may be averaged at 39 inches, of 

 which at least one-fourth, or ten inches, is lost by evaporation. 

 The entire amount of its rainfall would therefore amount to 31,- 

 449,600,000,000 gallons per year, or an average of 86,163,287,671 

 gallons per day. Hence by the received formula Q = 62.15 A 

 [I R — E], where Q is the daily supply in gallons, A is the catch- 

 ment area in acres, E. is the average annual rainfall, and E the loss 

 by evaporation, both in inches,* is obtained the collectible quantity 

 in Pennsylvania, viz : 41,526,144,000 gallons f)er day. Assuming 

 that one-half of that quantity reaches the surface at a useful height 

 above sea level and could be all converted into effective power with 

 an average head of 150 feet, the total available power expressed in 

 horse powers would be 524,320 HP per day, being equal to the 

 power obtained by the combustion j^er year of 3,075,698 tons of 

 coal of 2240 lbs. each, which is probably less than one-tenth of the 

 tonnage actually required and consumed in Pennsylvania to-day. 



There are, however, certain conceivable physical results that may 

 and to some extent must follow the combustion and dispersion 

 in the atmosphere of all the carbon now fixed in a form available 

 for fuel, which, though perhaps not at present fully computable, are 

 of the very highest consequence. It may be safely assumed that 

 such carbon, as well as that which is fixed in the calcareous or 

 other carbonates, was for the most part so fixed long after the earth 

 had condensed to its present form and dimensions and had cooled 

 sufiiciently to acquire a stable crust. Before that time the greater 

 part or all of such carbon had existed in atmospheric suspension 

 and whenever these compounds shall be resolved it must return to 

 and remain in the atmosphere, until again fixed by the slow and 

 gradual medium of chemical reaction in one case and the opera- 

 tions of vegetable life in the other. Since, however, our present 

 concex'n is with the coal, the end of which, however more or less 

 remote, we can with certainty foresee, let us endeavor to calculate, 

 though with much necessary recourse to hypothesis, whether any 

 appreciable efiect on the atmosphere and on animal life is likely to 



* Theory and Practice of Hydro-Mechanics, Inst. C. E. p. 44, cited in Ency. 

 Erit., article " Water Supply." 



