RED FOGS AND SEA DUST. 
103 
in the atmosphere and the occurrence of these showers, though it 
does not enable us to determine the true rate of motion in the gen- 
eral system of atmospherical circulation, yet it assures us that it 
is not less on the average than a certain rate. 
I do not offer these remarks as an explanation with which we 
ought to rest satisfied, provided other proof can be obtained ; I 
rather offer them in the true philosophical spirit of the distin- 
guished microscopist himself, simply as affording, as far as they 
are entitled to be called an explanation, that explanation which is 
most in conformity with the facts before us, and which is sug- 
gested by the results of a novel and beautiful system of philosoph- 
ical research. ^ 
170. Thus, though we have tallied the air, and put labels on 
the wind, to " tell whence it cometh and whither it goeth," yet 
there evidently is an agent concerned in the circulation of the at- 
mosphere whose functions are manifest, but whose presence has 
never yet been clearly recognized. 
171. When the air which the northeast trade-winds bring down 
meets in the equatorial calms that which the southeast trade- 
winds convey, and the two rise up together, what is it that makes 
them cross ? where is the power that guides that from the north 
over to the south, and that from the south up to the north ? 
The conjectures in the next chapter as to " the relation between 
magnetism and the circulation of the atmosphere" may perhaps 
throw some light upon the answer to this question. 
