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AUGUST, 1876. 
SPRINGS — Continued. 
T. A. FELCH, M. D. ^ . M 
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Thermal springs afford a very interesting subject of study. An>/^^| wafet 
is regarded as thermal whose temperature exceeds that of the surrounding air or 
ground. Perhaps 85° F. would be a proper limit to fix as a standard, and all 
below this must be considered as temperate or cold springs. As may, readily be 
conceived the zone of mean temperature, that is, the distance beneath the surface 
at which an unvarying temperature is found, varies in different localities. In Great 
Britain it is between 200 and 300 feet, in Paris about 50 feet and the same dis¬ 
tance in many parts,of this continent. From that distance as a standpoint it is 
found that there is a steady increase of temperature of i° F. for every 52 feet of 
descent. Therefore it may be said, in a general way, that the degree of warmth 
shown by the water upon its emergence may be taken as an indication of the depth 
of its source. But that would be a statement to which there are some exceptions, 
for there are other causes which influence the amount of heat. First, the water 
must be thoroughly and equally heated in its subterranean reservoirs; second, it 
must have a free and direct communication from its origin to its exit; and third, 
it must be present in such quantities and be expelled with such force as will enable 
it to retain its heat within itself and impart the least possible amount to the cooler 
strata and water above. These condition^, accordingly as they are fulfilled moi;e 
or less perfectly, give us the different grades of thermal springs. All degrees of 
temperature are represented, from the slightly warm to the boiling water. 
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