369 



The residuum of the evaporated rain-drop of January 12 showed itself about 

 in the manner seen in Fig. i. If the window-pane is used as a slide and the 

 dust examined directly with the microscope, one will find there a great number 

 of little drops ib/>, Fig. i), in most of which a very fine sediment is seen of the 

 constituents of the ashes ; in a few drops, however, there are to be found crystals 

 of common salt fdd); further, many loose crystals spread over the whole space (cc). 

 Probably the little drops are due to the presence of some hygroscopic matter 

 such as MgClj or CaCIj around some salt crystals. Especially at the lower end of 

 the whole drop assemble the larger, glassy, black and brovvn particles of the ashes. 



rig.i. 



..U:. 



/.; 



r. ■:■ ... 



VFir.u. 



/:: .,Q..,^....i 



Fig. I. — Sediment and residue of an evaporated drop of raiii, fallen January \z, 1S84. on a window-pane. 

 « « w. particles of the ash; h b, drops of hygroscopic matter; c <; r, crystals of common salt and andesitous 



mineral; t/ c', drops with salt crystals. 



Fig. 2 (X 400). — Crystalline matter in the residue of Fig. i. A, crystals of common salt; U, crystals of the 



andesitous mineral, insoluble in water. 



The above proves that during the last few weeks crystals of a i)articular 

 nature were floating in the air, and will perhaps explain the appearance of mock 

 suns described by some of the observers of the after-glow. 



In a sample of original ashes trom Krakatoa, when examined in oil. I only 

 found very few salt crystals, and the completely outgrown andesitous crystals not 

 at all. I am, however, convinced that with longer research I should have found 

 the latter, and others seem to have discovered them indeed, but they are without 

 doubt very rare. So it seems to me that it may be taken for granted that in 

 the atmospheric dust the proportionate number of completely formed crystals is 

 larger than in the natura! ashes. and the presence of so much common salt in 

 the upper air during these days is surely a remarkable fact. 



M. VV. Beijerinck, Verzamelde Geschriften;' Eerste Deel. 



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