150 AXXALS XEW YORK ACADEMY OF SCIEXCE> 



and the areas covered by negatiTe dei^aitiires antipleions. On the ciiTves 

 of overlapping means, the crests correspond to pleions and the depressions 

 c-orrespond to antipleions. I have presumed that the excess of pleions 

 over antipleions. corresponding to pleionian crests of eqtiatorial stations, 

 may be due to an increase of the solar constant.^ 



Eecently. many papers have been published about the influence of 

 volcanic dust on meteorological phenomena, on atmospheric temperature 

 m particular. I will simply cite the extensive researches of W. J. 

 Humphreys.® C. G. Abbot and F. E. Fowle' and of H. H. Kimball.^ 

 Humphreys, in particular, does not hesitate to admit ''that volcanic dust 

 must have been a factor, possibly a ver^' important one, in the production 

 of many past climatic changes." 



The hypothesis ascribing the origin of climatic variations to the pres- 

 ence of volcanic dust veils in the higher atmospheric layers is a very 

 ])lausible argument against my supposition that the changes in terrestrial 

 temperature are due to cosmical causes. Before goiQg any farther in. 

 my researches on the mode of formation and the dynamics of pleionian 

 variations, it was therefore necessary to find out to what extent one may 

 be justified in supposing that the antipleionian depressions of tempera- 

 ture are simply caused by the presence of volcanic dust veils. 



In this paper I will show that though, ia some cases, volcanic eruptions 

 may have influenced atmospheric temperature very greatly, this cause of 

 cjimatic variations is purely accidental and secondary, and that the 

 pleionian phenomenon is independent, in its cause, of the occurrence of 

 volcanic dust veils. 



YoLCAXic Ekuptioxs or the Yeahs 1883, 1902 axd 1912 



Although we know, from geological records, that the volcanic activity 

 of the earth's crust has undergone important changes, and although the 

 historical data indicate that seismic and volcanic phenomena have varied 

 in intensity and frequency, our knowledge of these fluctuations, of long 

 as well as of short duration, is most unsatisfactory. 



Papers on a possible relationship between sun-spots and volcanic phe- 



^ Hexetk Arctowski : "About Climatic Variations." Amer. Jour. Sci., vol. 37. p. 305. 

 1914. 



* W. J. HuMPHBETS : "Volcanic Dust and Other Factors in the Production of Climatic 

 Chanses and Their Possible Relation to Ice Ages," Bull. Mount Weather Observatory, 

 vol. 6. p. 1. 1913. 



^ C. G. Abbot and F. E. Fowle : "Volcanoes and Climate." Smiths. Misc. Coll., voL 60, 

 No. 29. 1913. 



* Herbert H. Kimball: "The Relation Between Solar Radiation Intensities and the 

 Temperature of the Air in the Northern Hemisphere in 1912-1.3." Bull. Mount Weather 

 Observatory. voL 6, p. 205. 1914. 



