Valley of the Mississippi. 



51 



Proceeding in our comparison we come next to St. Louis on the 

 Mississippi, in latitude 38° 36' N. ami 12° 15' of longitude west 

 of Cincinnati. But as the mean temperature of this parallel on 

 the coast, has not been ascertained by observations, it must be done 

 by the rule above prescribed. Taking, therefore, Philadelphia 

 in latitude 39° 56' (53.9° mean temp.) and Williamsburgh in lati- 

 tude 37° Iff (58.1° mean temp.) the mean will be 38° 36', cor- 

 responding exactly with the latitude of St. Louis ; and the proba- 

 ble mean temperature at this point will be 56.1° ; only one-tenth 

 of a degree higher than that of the latter place. The limited num- 

 ber of observations prevent tho application of the second part of 

 the formula, in order to ascertain the corresponding difference of 

 latitude. This difference is, moreover, so very trifling, that it 

 would not only be difficult but useless to settle it. 



The next and last point of comparison is Council Bluff, in lati- 

 tude 41° 31' N., and whose mean heat is 49.2°. And here I must 

 again resort to the method of calculation above adopted. By com- 

 paring therefore New-York, latitude 40° 40' (mean temp. 53.8°,) 

 and Albany, latitude 42° 39' (mean temp. 48.7°,) the mean latitude 

 will be 41° 40', and the probable mean temperature of this point 

 will be 51.2°. But this point is nine minutes north of the parallel 

 of Council Bluff; and calculating from the whole difference be- 

 tween the mean temperature at Albany and New-York, the differ- 

 ence of mean temperature of latitude 41° 40 7 and 41° 31' will be 

 about 00.5°. Adding this to 51.2° will give us 51.7° as the 

 probable mean temperature of latitude 41° 31' on the coast. 



From these comparisons therefore, which are as correct as the 

 limited number of observations will admit, it appears that the mean 

 temperature of Cincinnati is the same as that of the corresponding 

 latitude of the Atlantic coast ; of St. Louis one-tenth higher ; and 

 of Council Bluff two degrees and a half lower. And hence taking 

 the mean of all the differences obtained from the above data, it may 

 be assumed that the temperature of the valley of the Mississippi 

 from latitude 38° 36' to 41° 31' N. and from longitude 84° 27' 

 to 96° 42' W. is eight-tenths of a degree lower than that of the 

 Atlantic coast. 



It will be observed that 1 have thus far only treated of the annual 

 temperature of these places. I shall therefore next compare the 

 different eeasons ; for the temperature of the cycle of vegetation, 

 upon which depends the growth of plants, may be very different in 

 p)are« having the same mean annual temperature. 



