18 



Tbe Vegetation of the 



The means of the year are decreasing from east to west; in the same 

 way lower the temperatures of the winter, but the summer is the hottest 

 on the Mississippi and on the IlliipLois, well considered that Steubenville 

 and Nebraska City be on a greater elevation above the sea-level, and that 

 the climate of Steubenville is influenced by the Canadian lakes. 



By a mean period of frost of one hundred and eighty-three days for 

 the season free of frost one hundred and eighty-two days would be left, 

 and so the year would equally be divided; but as the last frost day in 

 thirty years occurred on the 11th of May and the first on the 1st of Octo- 

 ber, there would be left only one hundred and forty-two days, and even 

 that is good only for the locality of the observations in the midst of the 

 city, for on exposed places in the open country, even in this period, frosts 

 may occur, and, indeed, on the 4th of June, 1859, when the thermometer 

 in the city showed a mimimum of 35°, and on the 29th of August, 1863, 

 when the mercury went down to 41°, frosts were reported from the sur • 

 rounding country. Moreover, the so-called " white frost " may be formed 

 at a temperature of the air above freezing point. All bodies radiate heat, 

 and their temperature lowers, when they do not receive a fresh supply of 

 heat from outside. So do the plants at night time. Radiation takes place 

 in all directions to the surrounding air, and the more so the more clear 

 the sky is and the more calm the air. A small thermometer placed in the 

 grass, on an unprotected place, may very likely show ten or more degrees 

 less than that one that is suspended five feet above the ground. The 

 plants exhale constantly water in gas form, which precipitates upon the 

 cooled surface, and when that cooling reaches the freezing point, white 

 frost is formed. 



The difference of temperatures observed in localities of the same lati- 

 tude shows, that meteorological observations of one locality are good only 

 for that locality, and perhaps its next vicinity, and it is lost labor to com- 

 pute averages for wider districts f . i. of the State of Illinois, divided by 

 straight lines in a northern, central and southern part, or for even larger 

 area of five or six States, comparing the results with the crops of the same 

 districts so different, not only of temperature and precipitation, but in the 

 nature of the soil. There is no more sense in jt than would be in compu- 

 ting the temperature of the whole of North America. It is only waste of 

 time and paper. 



The means of the single years range between 8°, the lowest mean 

 temperature of a year was that of 1857^48.7; the highest that of 1878= 



