38 The Climate of Peoria. 
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 Illinois, well considered that Steubenville and Nebraska 
City are 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 183 days for the season free of frost, 182 days 
would be left and so the year would equally be divided; but as the last frost 
day in 30 years occurred on the 11th of May and the first on the Ist of Octo- 
ber, there would be left only 142 days and even that is good only for the local- 
ity 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 minimum of 35, and 
on the 29th of August, 1868, when the mercury went down to 41, frosts were 
reported from the surrounding 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. A small thermometer placed 
in the grass on an unprotected place may very likely show 10 or more degrees 
less than 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 latitude 
shows that meteorological observations of one locality are good only for that 
locality and perhaps its next vicinity, and it is lost labor to compute averages 
for wider districts; for instance, of the State of Illinois divided by straight 
lines in a northern, central and southern part, or for even larger areas of five 
or six states, comparing the results with the crops of the same districts so dif- 
ferent not only of temperature and precipitation but in the nature of the soil. 
There is no more sense in it, than would be in computing 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 degrees. The lowest mean 
temperature of a year was that of 1857 =48.7; the highest that of 1878 
=656.7. The mean of the first 10 years was 52.1; of the second 51.4; of the 
last 52.7. 
BAROMETER, 
The observations on the pressure of the atmosphere comprise 25 years from 
December 1860 to November 1886. 
The mean reduced to freezing point was 29.628 inches; the mean at 7 A.M, 
is 29.644; at 2 P.M. 29.606; at 9 P.M. 29.634. The highest stand was observed 
in January 1866 30.671, and the minimum in April 1880 =28.581, the 
range being 2.090. The greatest range in one month was observed in January 
1866 =1.676; the smallest in August 1878 =0.288. The highest mean of a 
month had December, 29.698; the lowest May 29.548. The greatest range in 
24 hours was observed in January =—1.028; in July it is only 0.389. ) 
There are generally two oscillations in 24 hours with two minima at 11 A.M. 
and 10 p.M., and two maxima at 4 A.M. and 4Pp.M. The rise and falling is in 
the tropic countries so regular that is possible to determine the day-time from 
the stand of the barometer; in our zone it is more variable, so that often a 
continuous falling or rising for several days is observed. 
PRECIPITATION. 
The mean quantity of rain and melted snow was 35.6 inches per year in 100 
rainy days. The smallest quantity falls in January 1.6 in 7 days, the greatest 
