364 | GEOLOGY OF OHIO. 
and fans are the powers applied to produce artificial ventilation. Fre- 
quently, exhaust steam from the steam-pump at the bottom of the upcast 
or pumping shaft is applied; but while this is a valuable auxiliary, it is 
too weak a ventilating force in a large and extensive mine to be used 
alone. 
The furnace has long been the favorite method of producing ven- 
tilation among practical men, but of late years exhaust fans of the 
Guibal, Schiele, Waddle, and other patterns have been introduced, and 
have worked so successfully as to supplant the furnace nearly altogether 
over large and important mining districts in England and the other 
continental States of Europe. ‘The furnace in its first cost is cheaper 
than the fan, and in deep mines is capable of doing equally effective 
work, while in shallow mines the fan is both cheaper and more effective 
as a ventilating power. The furnace is likely, however, to continue a 
ventilator as long as coal mining is followed. 
The proper construction of a ventilating furnace is a debutable ques- 
tion among mining engineers. A thin, wide fire, and low arch more effect- 
ually heat the passing current of air, than a furnace having a high arch. 
The arch, in my judgment, should never be higher than 3% feet above the 
bars, and the wider the furnace is, the better, and the whole width 
should be kept constantly and uniformly heated. As furnaces are 
ordinarily built they do not admit the whole amount of air which they 
are capable of moving; hence, it is found to add to their ventilating 
power to provide side chambers. The object of these chambers is to 
