HOW THE SUN "WARMS THE EARTH — ABBOT 



163 



They are produced by ab- 

 sorption of gases such as 

 hj'drogen, calcium, iron, 

 magnesium, and others, 

 which are volatilized in the 

 sun itself. Fourth, you 

 may note that though all 

 of the energy curves are 

 of nearly equal height in 

 the highest parts of the 

 infrared spectrum, their . 

 heights increase consider- 

 ably from the bottom en- 

 ergy curve shown to the top 

 one, if observed in the vio- 

 let or ultraviolet. This in- 

 dicates how much more 

 transparent our atmosphere 

 is for red and infrared rays 

 than it is for violet and 

 ultraviolet rays. The curves 

 were made successively, the 

 lowest in the early morn- 

 ing, when the sun shone 

 obliquely through a great 

 thickness of atmosphere, 

 causing much depletion of 

 the rays, and the highest 

 near noon, when the sun 

 was nearly vertically over- 

 head and the thickness of 

 air traversed was much less. 



SOLAR ENERGY SPECTRA 

 IN FREE SPACE 



By measuring the heights 

 of all of these curves at 

 some 40 points scattered 

 from the ultraviolet to the 

 infrared, and knowing the 

 thickness of atmosphere 

 traversed by the sun rays 

 in each instance, we are able 

 be at all points if taken in fr 



72774—36 12 



i-M \ t 



/''p> 



'f', 



to compute how high the curve would 

 ee space outside our atmosphere. 



