[ 2 99 ] 
the fame phenomenon in different parts of the coun- 
try at the time above-mentioned. 
Mr. Brown having omitted to mention, how the 
wind did blow at the time the black duft was ob- 
ferved, I made particular inquiry about that circum- 
ftance, and found it was from the S. W. which does 
not feem to favour the opinion, that the duft pro- 
ceeded from an eruption of mount Hecla, which lies 
about N. W. from Zetland ; unlefs it may be fup- 
pofed, that a north wind happening juft before had 
carried this duft to the fouthward, and the fouth- 
weft wind immediately following had brought it 
back to the northward. But, in this cafe, would 
not this black duft have been obferved in Zetland at 
its firft travelling to the fouthward ? Upon inquiry, 
I did not hear it was. 
Thus far I have obeyed your commands, which 
I will always do with pleasure ; and if you think it 
worth while to lay this letter before the Royal Society, 
I leave you at full liberty to do fo, or not, as you think 
proper : but what it contains may be relied on as 
truth. I am, with great regard, 
Dear Sir, 
Your moft obedient humble Servant, 
And. Mitchell. 
P-. S. I may add, that the diftance from mount 
Hecla to Zetland is between yoo and 600 
miles. 
Q^q 2 
xxxviir. 
