THE SUN-SPOT PERIOD. 149 



the earth would, if allowed sufficient time, take up a new mean temperature T such 



199 /'199\i_ 



that (T)*+=2QQ (290)*+ or T=290°f goo/"^' ^^"^ ^ ^^'^"^'^ ^® ^^"^^ *° ^^ exceed- 

 ing 289°. 97, and the fall of temperature directly due to the sun spots would be only 

 0°.03 or less. This line of argument is substantially that adopted by Professor 

 Poynting, Philosophical Transactions, Series A, vol. 202, p. 530, 1903. 



It would therefore appear that the direct effect of sun spots is far smaller than that 

 observed by Nordmann. But it is entirely possible that the increased a1)sorption of 

 the sun's envelope, which he mentions as probably attending them, may produce the 

 effects found. See in this connection Halm's article, "A New Solar Theory," Smith- 

 sonian Reiwrt, 1902, and also S. P. Langley, Astrophysical Journal, June, 1904. 



