A STUDY OF COKRKLATIONS AMONG TERKliSTKIAL TEMPERATURES. 385 



§ 1 8. Comparison with Results of Langlnj's Work of 1903. 



Although the writer deems it appropriate for the most part to leave the farther 

 discussion of his results, and their comparison Avith the views of others, to other 

 investigators, an exception may well be made in the case of the very suggestive paper 

 of Langley.* It should be premised that Langley does not present his results as con- 

 clusive, but only as showing seeming correlations between temperatures and bolometric 

 measurements of the sun's radiation, the results of which should be tested by further 

 researches. He gives the following general summary of his conclusions : 



" A series of determinations of the solar radiation outside the atmosphere (the 

 solar constant), extending from October, 1902, to March, 1904, has been made at the 

 Smithsonian Astrophysical Observatory under the writer's direction. 



"Care has been exercised to determine all known sources of error which could 

 seriously aflFect the values relatively to each other, and principally the varying 

 absorjDtion of the Earth's atmosphere. Though uncertainty must ever i-emain as to 

 the absorption of this atmosphere, different kinds of evidence agree in supporting the 

 accuracy of the estimates made of it and of the conclusions deducted from them. 



" The effects due to this absorption having been allowed for, the inference from 

 these observations appears to be that the solar radiation itself fell off by about 10 per 

 cent., beginning at the close of March, 1903. I do not assert this without qualification, 

 but if such a change in solar radiation did actually occur, a decrease of temperature 

 on the Earth, which might be indefinitely less than 7°. 5 C, ought to have followed it." 



The present writer understands that not only Langley's work with the bolometer, 

 but observations by actinometric methods showed a remarkable diminution of the 

 solar radiation, extending from some time in 1902 through a considerable portion of 

 1903. But as such observations are made only on the radiation which reaches the 

 earth's surface the results still leave open the question whether the change was in the 

 sun itself or was caused by increased absorption in the earth's atmosphere. The 

 apparent diminution during the period in question has been plausibly attributed to 

 the absorbing matter thrown up by the eruption of Mount Pelee on May 8, 1902. 

 If the diminution of radiation was only apparent, being due to the absorption, we can- 

 not, in the present state of science, decide whether there would be any effect upon 

 terrestrial temperatures. While less heat would reach the earth directly, more would 

 be absorljed in the middle regions of the atmosphere ; and this would apply both to 

 the absorption of the sun's rays and of the heat radiated from the solid earth. The 

 vapors of Mount Pelee, if they had any influence whatever, might, so far as we know, 



* "On a Possible Variation of the Solar Radiation and Its Probable Effect on Terrestrial Temperat'ires, " Astro- 

 physical Journal, June, 1904. 



