The Press., 1915-03-03
HEAT OF OUR SUN
To Measure It Is a Perplexing
 Problem For Science.
NEWTON ONCE TRIED TO DO IT
He Figured It at the Amazing Intensity of f,66e, 300 Degrees csntisrade, While the Latest Estimates Place it at About 6.5oo Degrees.


 How hot, is the sun? The question has been answered in many different ways. and it Is by no means certain that we have yet arrived at an even approximately accurate answer. Yet 1t would seem that. as the sun Is the only source of the earth's heat. and as we know the exact distance of the sun. 1t ought to be easy to calculate bis heat That Is what Newton thought in 1880 when. finding that thermom, eter registered 65 degrees c. in the sun and 29.44 degrees 0. in the shade. and applying the law of the square of distance Ne announced that the suns heat was l.669. .30O degrees C.!
 In 1887 Sir John Herschel and Pouil- let devised special instruments for measuring the solar heat. but at the very beginning disagreed on funda mental question Pouillet wanted to estimate that the earth's atmosphere cut off half the suns heat; Herschel insisted that 1t cut of only one-third. Herschel reached the conclusion that the suns Heat was two caIories per square centimeter per minute. Pouil let calculated it at 1.7633 calories per square centimeter per minute. This means that the suns rays falling yer tically upon each square centimeter of the earth's surface would be sufficient ly powerful. if it were not for their absorption by our atmosphere. to raise 1.7633 grams of water one degree c per minute This number is what as tronomers call the solar constant
 Pouillet's figures. IT. were generally accepted until recently Forbes by ex periments at the top and at the base of a high mountain calculated that 2.So was the correct number. violle made 1t 2.54. and Crova asserted that it was certainly superior to two calories per square centimeter per minute.
 The American Langley inverted the bolometer. by means of which he measured the intensity of each ray by the length of its wave before entering our atmosphere. Thus be proved that the rays Of shortest length are those that are most absorbed It is as if we placed two red glasses between our selves and. the sun. one representing the suns atmosphere and one repre- senting our own
 The Abbe Moreux. director of the Bourges observatory. declares in an article in Cosmos that if these two at mospheres were eliminated and We could see the sun as he really Ia hr would appear to be a brilliant greeniSh blue.
 Langley's calculations placed the SD lar constant at about three He proved that scarcely to per cent of the suns rays penetrated to sea level.
 Other observers obtained other hg ures, and at the beginning of this cen tury the tendency was to return to those announced by Herschei and Pouillet.
 It Is certain that the earth intercepts only about one two-billionth part of the actual heat of the sun. but if We adopt Langley's figure. 5, we find that the fraction of heat received would be sufficient to melt annually layer of ice 222.75 feet thick at the equator of the earth. The average power receiv cd from the sun over the entire earth is equal to l54.464.O 900 kilogrammeters a year, or one continuous horsepower for every l.72 square meters.
 The greater part of this neat Is used mp In keeping the earth warm; but. Nc cording to Helmholtz, about thou sandtb part of 1t is absorbed by ami mals and vegetables and becomes an abundant reserve of energy for the human race.
 If We accept the more recent figures, which are the result of the calculations of Messrs. Abbott. Fowle and Aldrich at the Smithsonian institution ID Washington and call the solar constant two calories per square centimeter per minute the results are scarcely less striking.
 If the total heat could be applied to a block of Ice at o degrees c. as thick ss the earth-S.0OO miles-this would De entirely melted in a quarter of an hour All the water thus obtained would be turned to steam at 100 de srees c. 117 minutes later the whole operation from ice to steam having taken only two hours and twelve min utes
 The most recent estimate of the tenn Derature of the suns surface Is be- tween 5000 and 1000 degrees O-New fork World.
 His One Regret.