Meteorological Observations at Hudson, Ohio. 317 



of the same depth, the surface of the earth at A being fourteen 

 higher than at B. The entire range of A is 1°.6, of B 3°.6. 

 The water of the two wells is very unlike. I hence infer that 

 they are fed by different springs ; and as the annual change in 

 the temperature of A is less than that of B, I conclude that the 

 springs of A are the deepest, and hence have a higher tempera- 

 ture. It would seem, then, that wells do not necessarily indicate 

 the mean temperature of the earth at the same depth. Their 

 temperature depends partly upon the depth of the springs by 

 which they are supplied. Which well then represents most 

 nearly the mean temperature of the earth at the same depth ? 

 In ray opinion it is the well B; for its depth of water is almost 

 quite invariable, and the autumn of 1S3S was a period of nearly 

 unprecedented drought. 1 think then the depth of its springs 

 cannot be less than forty or fifty feet. The water of the well 

 A, I infer, comes from about twice that depth. Assume that the 

 mean temperature increases 1° F. for every forty feet below the 

 surface, and we have 1°.2 correction for a depth of forty-seven 

 feet. Subtract this from 49°. and we have 47°.8, the mean 

 temperature of the earth's surface by the well B. The mean 

 between this and the former result is 47°.6, which is probably 

 a near approximation to the mean temperature of the place. It 

 will be observed that both of the wells indicate an increase of 

 temperature for each of the last two years, and by precisely the 

 same quantity. The same is also seen in the daily observations 

 on page 315. The mean temperature of the three years at 9 

 A. M. was 47°.9; 48°.8 ; 49°.0. 



The following table exhibits all the days in which the ther- 

 mometer has fallen to zero. 



The following table exhibits all the days in which the ther- 

 mometer has risen to 90°, all being in 1838. 



