THOUGHTS ABOUT KRAKATOA. 



33? 



had sufficiently expanded from its original tropical limits 

 to include Europe and the greater part of North America. 

 During the winter months the suspended material gradu- 

 ally subsided or, at all events, became evanescent, and in 

 the following spring the earth regained its normal state 

 in so far as the Straits of Sunda were concerned (Fig. 21). 

 It remains to give some brief account of the optical 



APPROXIMATE NORTHERN UMIToFTNE MAIN SKY PHENOMENA AT THE END OF NOVEMBER 1863. 



/I MSf rct 



Fig. 21. 



phenomena due to the presence of dust, unusual both in 

 quantity and in character, in the upper atmosphere. The 

 frontispiece of the volume shows some beautiful pictures 

 of the twilight and after-glow effects as seen by Mr. "W. 

 Ascroft on the bank of the Thames a little west of London, 

 on the evening of November 26, 1883. Analogous phe- 

 nomena to those here depicted were seen almost univer- 

 sally during November and December in the same year. 



