J. FE. Willet on Indian Summer. 345 
‘ =e 
consist of minute fragments, in some 
in others of the ashes of volcanoes.” 
known as Indian Summer might be produced by the burning of 
the prairies, was not thought worthy of any comment, yet the 
advance of science in revealing the facts I have stated, renders 
this hypothesis by no means unworthy of attention.” 
Although these extraordinary fires may furnish the smoke for 
_ &xtraordinary manifestations of smokiness as in “dry fog” or 
_ Unusually dense Indian Summer, yet I think too little impor- 
| _ tance has been attached to the smoke from ordinary fires. 
) _ Mense volumes of smoke ascend daily from these, and it is not 
improbable that the majority of smoky days derive their smoki- 
| from these ordinary sources. Zs 
_2. Atmospheric currents, subsiding from higher to lower re- 
, gions, would produce smokiness by depressing the smoke, and 
a by coming under greater pressure would become relatively dry, 
4nd would thus produce relative dryness and equableness of 
‘emperature during their continuance. ; oe 
Every meteorologist has, doubtless desired an indicator or 
Vane for descending currents. Can’ any be devised more sensi- 
_ lve than smoke? The direction of horizontal currents is con- 
_ Santly determined by the swaying wreaths of smoke from chim- 
_ heys. If the rising columns of smoke remain suspended in the 
T atmosphere and hang like a smoky veil over the whole 
: landscape, why may not the phenomenon be referred to descend- 
