196 Examination of some Atmospheric Dust. [Feb. 



3. The fibres, which one would assume to be capillary obsidian, if 

 we supposed the dust volcanic, are not so, but apparently animal ! burn- 

 ing up with the common ammoniacal smell and smoke of burnt hair or 

 feathers. 



4. On charcoal the assay burns up as before, leaving a coherent, 

 olive-grey, granular mass like pumice, which is infusible. 



5. With Soda on charcoal this fuses to a reddish, dark grey, opaque 

 and pearly bead with violent spitting and throwing up of l^tle globules, 



6. When to this bead is added an equal quantity of Borax, it fuses 

 on Platinum wire to a transparent bright and colourless, but crackly 

 glass, which is slightly green while cooling. 



As far then, as physical and chemical characters are concerned, we 

 may call our dust a congeries of light downy fibre or hairs with silex 

 adhering to them and an admixture of an alkaline salt ! It appears from 

 Dr. Macgowan's and Dr. Bellott's letters that the mist and dust cer- 

 tainly extended on the same day from Ningpo in about 30° N. Lat. ; to 

 Shanghae in 31|° N. (I use round numbers here) which gives 90 miles 

 of difference of latitude, and that it was noticed with light winds from 

 N. N. E. toE. N. E. from 8 A. M. to 1 A. M. or for 17 hours. Now if 

 we take it to have moved only at the rate of 2\ miles per hour, as " the 

 sand passed the ships in light clouds," says Dr. Bellott (and this is the 

 slowest rate we can assign to moving clouds,) this would give 17*2| or 

 42 miles in length for it, and without noticing the difference of longi- 

 tude between Ningpo and Shanghae, which are nearly N. W. and S. E. 

 of each other, we may say that the difference of latitude, 90 miles, was 

 the breadth. We have thus 90 * 42| or 3825 square miles for its extent ! 



Where could a cloud of 3800 square miles of fibres, alkali, and sand 

 (for this it was by the specimens before us) come from ? 



We have seen that it is not in the least volcanic, its animal nature 

 putting this wholly out of the question, and all the volcanic dusts upon 

 record are for the most part fusible and pulverulent (like pumice or 

 obsidian) while the residuum of ours is perfectly infusible— for the 

 little globules are, as I have stated, properly the only fusible parts, being 

 the alkaline concretions. I shall now proceed to show that though the 

 wind was from the N. E. and the phenomena occurred while the N. E. 

 monsoon was yet blowing, that in all meteorological probability the 

 dust did not come from the N. E. but from the N, W. or W, N. W. 



