386 



SCIENCE 



[N. S. YoL. XXXVI. No. 926 



Sir William Ramsay has made a very 

 careful study of the problem from the Eng- 

 lish point of view. He has considered the 

 various sources of energy, such as the tides, 

 the internal heat of the earth, the heat of 

 the sun, water power, the forests and even 

 atomic disintegration, and has come to the 

 conclusion that none can be practically 

 used in England on account of her special 

 contour and climate. 



Though the internal energy of the earth 

 may produce terrible disasters through vol- 

 canic eruptions and earthquakes, it can 

 hardly be used by man. The energy de- 

 rived from the rotation of the earth (tides) 

 can hardly be counted upon on account of 

 the enormous quantities of water that 

 would have to be handled. Atomic disin- 

 tegration has recently been treated in a 

 brilliant lecture by Frederick Soddy, with 

 special reference to the enormous energy 

 changes which are involved. If man ever 

 succeeds in availing himself of the internal 

 energy of the atoms, his power will surpass 

 by far the limits assigned to it to-day. At 

 present he is limited to the iise of solar 

 energy. Let us see, however, whether the 

 actual energy may not supplant that stored 

 up in fossil fuel. Assuming that the solar 

 constant is three small calories a minute 

 per square centimeter, that is, thirty large 

 calories a minute per square meter or about 

 1,800 large calories an hour, we may 

 compare this quantity of heat with that 

 produced by the complete combustion of a 

 kilogram of coal, which is 8,000 calories. 

 Assuming for the tropics a day of only six 

 hours sunshine we should have, for the 

 day, an amount of heat equivalent to that 

 furnished by 1.35 kg. of coal, or one kilo- 

 gram in round numbers. For a square 

 kilometer we should have a quantity of 

 heat equivalent to that produced by the 

 complete combustion of 1,000 tons of coal. 

 A surface of only 10,000 square kilometers 



receives in a year, calculating a day of only 

 six hours, a quantity of heat that corre- 

 sponds to that prod^iced by the burning of 

 3,650 million tons of coal, in round num- 

 bers three billion tons. The quantity of 

 coal produced annually (1909) in the 

 mines of Europe and America is calculated 

 at about 925 million tons and, adding to 

 this 175 million tons of lignite, we reach 

 1,100 million tons, or a little over one billion. 

 Even making allowances for the absorption 

 of heat on the part of the atmosphere and 

 for other circumstances, we see that the 

 solar energy that reaches a small tropical 

 country — say of the size of Latium — is 

 equal annually to the energy produced by 

 the entire amount of coal mined in the 

 world! The desert of Sahara with its six 

 million square kilometers receives daily 

 solar energy equivalent to six billion tons 

 of coal! 



This enormous quantity of energy that 

 the earth receives from the sun, in com- 

 parison with which the part which has been 

 stored up by the plants in the geological 

 periods is almost negligible, is largely 

 wasted. It is utilized in waterfalls (white 

 coal) and by plants. Several times its 

 utilization in a direct form through mirrors 

 has been tried, and now some very prom- 

 ising experiments are being made in 

 Egypt and in Peru; but this side of the 

 problem is beyond my power to discuss and 

 I do not propose to treat it here. 



The energy produced by water power 

 during the period of one year is equal to 

 that produced by 70 billion tons of coal, ac- 

 cording to the data given in Professor 

 Engler's lecture. It is, however, very 

 small, as might be expected, in compari- 

 son with the total energy that the sun 

 sends to the earth every year. Let us now 

 see what quantity of solar energy is stored 

 by the plants: on the total surface of the 

 various continents, which is 128 million 



