HOW THE SUN WAKMS THE EARTH ABBOT 153 



IMMENSITY OF SOLAR RADIATION 



I despair of giving you a vivid idea of the immensity of the sun's 

 heat and of the quantity of enei<ry it continually emits. Experi- 

 ment: I turn on for an instant a 1,000-candlepower Mazda lamp. 

 It seems blindingly bright. But the sun's surface for equal areas 

 emits about five times as blinding a beam as this lamp does, and the 

 area of the sun's surface is about 8 billions of trillions (8X10-^) 

 times that of the lamp filament. Plateau, a Belgian physicist, 

 wished to study the after images left within his eyes by a bright 

 light. Looking steadil}^ at the sun for 20 seconds, he lost his sight 

 completely. 



Dr. S. P. Langley describes how he made an experiment to com- 

 pare the rays of the molten steel poured from the Bessemer con- 

 verter with those of the sun. Into the enormous converter pot there 

 streamed first some 15,000 pounds of molten iron loaded with half a 

 ton of silicon and carbon. Then a blast of air was forced up 

 through the glowing mass, and the chemical action set up a heat 

 which so far surpassed mere iron-melting temperature that when 

 another 15,000 pounds of molten iron was added it looked like choco- 

 late poured into a white cup. The cataract of liquid steel was then 

 discharged, shooting showers of scintillations that seemed sunlike 

 in their brillancy, and spattering the surroundings for a hundred 

 feet with little shooting stars. But there was nothing really sun- 

 like at all in this fierce glare. For when Langley exposed an appa- 

 ratus which took a balance between the brightness of the surface of 

 the steel and an equal surface of the sun, the sun was found to send 

 out at least 87 times as intense radiation, square foot against square 

 foot, as the dazzling steel. This applies to the total rays, whether 

 visible to the eye or not. But for the light rays only, the sun 

 proved intrinsically not less than 5,000 times the stronger source. 

 And this was near Pittsburgh, where the sun's rays had already 

 lost over half their intensity in the murk of the atmosphere. 



SUN RATS EMITTED IN ALL DIRECTIONS 



Some people, possibly of Scotch ancestry, reluctant to contem- 

 plate a pitiable waste of good things, have supposed that the sun 

 does not send its rays in every direction, but only in those directions 

 where there lie objects to be shined upon, such as the earth or the 

 planets. This is not true. The sun shines nearly equally in every 

 direction, and for aught wo know the rays it is sending out at this 

 instant, if they hit nothing, may go on and on for a million years 

 or even forever, covering 186,000 miles on their journey every single 

 second that they travel. This thesis is proved by the observed fact 

 that the intensity of the sun's rays falls off as the square of its dis- 



