292 



TRANSACTIONS OF THE NORTHERN 



Table first has been elaborated from nearly four thousand observa- 

 tions, by the use of standard instruments under the direction of the 

 Smithsonian Institution, at Washington. These observations were made 

 at seven A. M., two P. M. and nine P. M. They^are a continuation of 

 Meteorological investigations begun twenty years ago, and form an un- 

 broken chain, began in eighteen hundred and fifty-two. Together with 

 the observations of others, they have established the mean annual 

 temperature in northern Illinois, and the annual mean rain-fall, in the 

 county of DeKalb, and those counties immediately adjacent. 



Many interesting facts may be gleaned in the pursuit of this kind 

 of knowledge, with patient study and perseverance. The table in 

 question shows first the march of temperature, which would form not an 

 imperfect curve, such is the regularity of its ascent and decline from 

 spring to autumn. What has hitherto seemed in physical nature to 

 have been capricious and subject to no fixed law, is now referable to 

 general principles, upon which these changes depend. 



The table presents first, three divisions, under heads of Ther- 

 mometer, Winds, and Weather, and if studied as grouped, will at once 

 lead to a full understanding of atmospheric phenomena, and physical 

 changes, with which it deals. First, under the appropriate heading, may 



