499 ENGELMANN-—MEAN & EXTREME TEMPERATE IN ST. LOUIS. 
slighter one in the two weeks succeeding them. After that the 
temperature sinks rapidly to about Dec. 10th, from which time 
till the beginning of February the changes are not very marked. 
The mean temperature of April 17th to 19th and from October 
12th to 17th correspond with the mean of the year. 
The tables, and still more distinctly the diagram, show us also 
that the extreme highest and lowest temperatures diverge most in 
winter and least in summer, and that their values are much more 
variable in the former than in the latter season. The possibilities 
of range from the middle of December to the middle of March are 
80 to 95 degrees, while in June and July they amount only to 4 0 
or 45 degrees. 
The same law is found when we compare the actually ob¬ 
served lowest minimum and highest maximum of every month ; 
their divergence is greatest in January, and least, not much more 
than half, in July. 
January. 
February - 
March. 
April. 
May. 
June. 
Min, 
Max. Range. 
72.0 94.5 
76.0 91.0 
86.0 86.0 
99.0 81.0 
97 5 68.5 
101.5 58.5 
July. 
August .... 
September . 
October .... 
November.. 
December.. 
Min. Max. Range. 
53.0 104.0 51.0 
45.0 104.0 59.0 
35.0 102.0 67.0 
19.5 91 0 71.5 
— 0.5 81.5 82.0 
—19.5 72.5 92.0 
Nearly the reverse is the case—i.e. the range in winter is much 
smaller than that in summer—if w r e compare the difference of the 
average daily minima and maxima for each month : 
January.. 13.27 I April..... 18.29 1 July.18.24 I October .. 18.00 
February. 14-72 May. 18.77 August... 17-75 November 14.06 
March- 16.40 | June.18.14 | September 19.05 | December. 11.97 
The range, it will be seen, is, on the whole, least in the cooler 
and greatest in the warmer months of the year; but this differ¬ 
ence is not due to the lower or higher temperatures of those 
months, for it will be seen that in December the range is the 
smallest (smaller than in January) and in September greatest 
(greater than in July). This variation in the range of maxima 
and minima is undoubtedly owing to the condition of the sky in 
the different months. Gloomy weather prevails in the beginning 
of winter, and a clear sky with abundant evaporation, and thus 
a reduction of night temperature, in the autumn. The little table 
can give us an indication of the prevailing weather in the differ¬ 
ent months. Thus the difference, and its cause, the clearness of 
