I. 



JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. Ill JULY 19, 1913 No. 13 



GEOPHYSICS. — Volcanic dust as a factor in the production of 

 climatic changes.^ W. J. Humphreys, Weather Bureau. To 

 be published as a Bulletin of the Weather Bureau. 



Geological investigations have given us a great deal of informa- 

 tion in regard to the cUmates of the past, and the following 

 tentative conclusions appear to be well established: (a) The cli- 

 matic changes were several, probably many. (6) They were 

 simultaneous over the entire earth, and in the same sense. That 

 is, colder everywhere at the same time (climatically speaking) 

 or warmer everywhere, (c) They were of unequal intensity. 

 (d) They probably were of irregular occurrence, and of unequal 

 duration, (e) They, at least one or more, progressed with sec- 

 ondary variations of intensity, or with advances and retreats of 

 the glacial edge. (/) They have occurred from very early, prob- 

 ably from the earliest, geological ages down to the present, and 

 presumably will continue irregularly to recur for many ages yet 

 to come. 



Many efforts have been made to find a probable and at the 

 same time an adequate physical basis for, or cause of the climatic 

 changes that are known to have occurred; but, one after another, 

 nearly all have been definitely and finally abandoned, either 

 because of inconsistency with known physical laws or because 

 they proved inadequate to meet the conditions imposed by geo- 

 logical investigations. 



1 Presented in substance before the Astronom'cal and Astrophysical Society 

 of America, at Cleveland, O., January 1, 1913. 



365 



