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 isless 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 my opinion it is the well B; for its depth of water is almost 
quite invariable, and the autumn of 1838 was a period of nearly 
unprecedented drought. I 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 sg .2 correction for a depth of forty-seven 
feet. Subtract this from 49°.0 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 
anear approximation to the mean temperature of the place. It 
will be observed that both of the wells indicate an increase 
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 exhiiee-ait the days in which the ther- 
mometer has fallen to zero. 
1838, Feb. 20, 10 rx, —1.0. 1840, Jan. 17, 7}a.m —6.2 
21, Of a.m. —6.0 18, 2am 0.0 
22, Tam —18 24, Tga.m. —1.9 
25, 634.m. —8.1 25, Tact ©" OD 
26, 6$a.m —0.2 1841, Jan. 3, Zam. —9.1 
1839, Jan. 23, Sr.m —-25 — 18, 744. m.—10.1 
Mar; 4; 64. m. —5.9 19, 6am —3.7 
1840, Jan: 16; 7 a.m. —9.1 
~The fe lowing table exhibits all the days in which the ther- 
PM Serge . ee Oe ° 
x2 
ea 
~ 
