Meteorological Observations at Hudson, Ohio. 279 
mometer sinks pretty uniformly until it approaches near the dew 
point, when it experiences an apparent resistance to further de- 
pression, refuses to sink any lower, and perhaps begins to rise ; 
butif you add ether sufficient to carry it below this point, it will 
probably sink several degrees at a jerk. The explanation I sup- 
pose to be the following. As the lower ball is cooled down nearly 
to the dew point, precipitation commences, though not’ perhaps 
in a visible ring. Heat is liberated which opposes the further 
depression of the thermometer, and more ether is required to 
counteract this effect. When this obstacle is overcome, the ther- 
mometer suddenly sinks several degrees. 
It will be observed that the diurnal range of the hygrometer is 
very small; less than 2° from 9 a.m. to 3 p.m. for the entire 
year. On clear nights the thermometer usually sinks to the dew 
point of the preceding day, and not much lower, for the liberated 
heat from the condensed vapor opposes its further descent. Here 
then we have a method of predicting the lowest temperature of 
the succeeding night if it-be clear; and this remark may be of 
considerable practical utility at times when vegetation is liable to” 
be injured by frost. If the hygrometer sinks to 40°, we may 
confidently expect frost in a clear and still night, although the 
thermometer of the preceding day may have been quite high; 
but as long as the hygrometer is high, there is little danger of 
frost. 
WINDS. 
The following table is constructed in the manner described in 
my former article, p. 320, and exhibits the results of seven years’ 
observations. 
Months. N = E. = a 
“hee 7a oF 04-4) 85: 4 230° 
1285) 107-5 200°4| 78 
ay, 113°7, 102°6| 91-8) 227-4) 85 
¥ ‘ 226: l/s. 81 
112 9 : 
1227-0 1425°8 92112742718. 85° 
Sum of 9 a. m. and 3 Pp. m— 
Course. 
N. Ss. E. W. 
31313 27848 1621:2 5826°5 n. 85° 17 w. 
