Meteorological Observations at Hudson, Ohio. 319 



sixty-six hours. Assume that each rain last six hours ; it is then 

 upon an average sixty hours between two successive rains. But 

 if the thermometer be 25° above the dew point, there must have 

 been a considerable interval since the preceding rain ; call it 

 twelve hours. Rain then falls upon an average in forty-eight 

 hours more ; that is, there is an even chance that it will rain in 

 twenty-four hours. If then it does not appear that extreme dry- 

 ness of the air constitutes any ground to expect rain, it is at least 

 worthy of notice that it furnishes no ground for anticipating that 

 it will 710^ rain. 



The following are the only instances in which the dew point 

 has risen to 80°, all in 1838, and observed at 3 P. M. 



July 10, 82°. 1 July 28, 80°.2 .^^ 



20, 80 .0 29, 80 .7 "^^ 



26, 80 .0 Aug. 6, 81 .8 



27, 80 .5 



In four of these cases a heavy thunder shower followed the 

 same afternoon. The following are the only cases in which the 

 dew point has sunk to zero. It should be borne in mind that 

 these observations are made only at 9 A. M. and 3 P. M. If they 

 had been made at sunrise the list would have been larger. 



1839. 1840. 1841. 



Jan. 23, 9 a. m. — 4'^.0 



3 p. M. —2 .0 



Feb. 5,3 p.m. —4 .0 



Nov, 25,9 A. M. — 5 .0 



Jan. 16, 9 a. m. — 4°.5 



3 p. M. — .4 



17, 9 A. M. —5 .0 



25, 9 A. M. —0 .7 



Jan. 3, 9 a. m. — 3o.O 



18, 9 A. M. —5 .0 



19, 9 A. M. —2 .0 



WINDS. 



The chief instruction to be derived from mean observations of 

 the winds is a decision of the question. In what direction does 

 the wind progress 1 This does not mean, towards what quar- 

 ter does the wind blow raosi frequently at a particular hour, or 

 at all hours, though some seem to have so regarded it. The 

 wind's force is an element in the inquiry no less important than 

 its direction. It is obvious that we cannot give a very exact and 

 satisfactory answer to this question without the aid of self- 

 registering anemometers. Instruments of this kind have long 

 been known, but for some reason appear not to have attracted 

 much attention until recently. It is hoped that those which are 

 now in operation will soon set the question at rest. Meanwhile 

 my own observations, made with a vane attached to a revolving 

 shaft, and in which the force of the wind is estimated by an 



