ARCTOWSKI, VOLCAXIC DUST VEILS 151 



iiomena have been published by E. Kluge,^ Joseph O'Eeilly/^ Charles 

 Zenger/^ H. I. Jensen^- and others. As will be seen later, a A^erv sug- 

 gestive conclusion may also be derived from the annual frequency list of 

 volcanic eruptions compiled by Leo Kelley. If, therefore, some striking 

 coincidences between changes of atmospheric temperature and the in- 

 crease of frequency or violence of volcanic eruptions exist, the existence 

 of these coincidences is a very inadequate argument in favor of the 

 liypothesis that the variations of temperature are due to volcanic dust 

 veils, since both phenomena, the volcanic paroxysms as well as the coin- 

 cident temperature changes, may be the effect of some common extra- 

 terrestrial factor. 



In this study, however, only the volcanic eruptions of an explosive 

 character have to be taken into special consideration. Moreover, it is 

 only when volcanic dust has been projected in great quantity above the 

 ordinary elevation of the cirrus clouds, that is to say to an altitude of 

 8,000 m. or higher up, that this dust could remain in suspension long 

 enough to be spread out all around the globe by the winds of the lower 

 stratosphere. 



In the case of the famous Krakatoa eruption of 1883, the optical 

 phenomena produced by the volcanic dust veil have been studied very 

 extensively. For reference it will be sufficient to cite the reports of 

 E. D. M. Yerbeekis and of the Eoval Societv.^* 



Krakatoa is a small island between Sumatra and Java and lies 6° S. 

 ]at. The explosion occurred on August 27, 1883. The main sky phe- 

 nomenon produced by the dust went around the world in fifteen days 

 from east to west along the equator, spread out north and south, was 

 observed in the Gulf of Mexico by the end of September and all over the 

 States in November. The extraordinary twilight phenomena have been 

 well described by J. Kiessling.^^ One of these phenomena, the Bishop's 

 ring, has been the subject of many investigations.^^ The actinometric 



^ E. Kluge : "Ueber einige neue Forschungen auf dem Gebiete des Vulkanismus," 

 Zeitsch. d. dent. geol. Ges., vol. 15, p. 377. 1863. 



i» Joseph P. O'Reilly : "On the Dates of Volcanic Eruptions and Their Concordance 

 with the Sun-spot Period," Proc. Roy Irish Acad., 3 ser., vol. 5, p. 392. 1899. 



" Ch. V. Zexger : "La theorie electrodynamique du monde et les eruptions volcaniques 

 et grands sismes," Assoc, frang. p. I'avancement des sciences, Sess. 33, p. 572. 1904. 



12 H. I. Jensex : "Possible Relation Between Sunspots and Volcanic and Seismic Phe- 

 nomena and Climate," Jour. Roy. Soc. of New South Wales, vol. 38, p. 40. 1904. 



"R. D. M. Verbeek : Krakatau. Batavia, 1885. 



" G. J. SvMOxs : The Eruption of Krakatoa and Subsequent Phenomena. London. 1S8S. 



1^ J. KiESSLixG : Untersuchungen iiber Diimmerungserscheinungen zur Erkliirung der 

 nach dem Krakatau-Ausbruch beobachteten atmospharisch-optischen Storung. Hamburg. 

 1888. 



i« J. M. Pernter : Meteorologische Optik, pp. 469, 769. Wien, 1902-10. See also — 

 Serexo Bishop : "The Origin of the Red Glows," Amer. Meteor. Jour., vol. 3, pp. 127. 

 193. 1886. 



