318 Meteorological Observations at Hudson^ Ohio. 



July 18, 910.2 July 28, 9F.5 



19, 91 .2 29, 91 .7 



26, 90 .7 Aug. 23, 90 .8 



27, 92 .0 



The greatest heat of 1839, was July 30, 88^.2 ; and of 1840, 

 July 16, 86°. 7. The entire range of the thermometer has been 

 102°. 1. 



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

 mometer has been 25° above the dew point, all occurring at 

 3 P. M. I have also given the interval between each of these 

 dates and the next subsequent rain. 



30.8 

 30.7 



in 8 hs. 



in 44 " 

 27.3 in 20 " 

 28.6|in 9 " 

 26 8 in 24 " 

 25.0 in 5 ds. 

 25 Ojin 24 hs, 

 28.2 in 40 " 

 27.4:in48 " 

 33.9 in 8ds. 

 25 8 in 6 " 



The greatest difference is 36°. 0. It will be observed that all 

 of the above cases, with two exceptions, occurred in the spring 

 of the year, and half of them in the month of April. This 

 affords the explanation of the remark before made, that April 

 was the driest month of the year. So far as these observations 

 afford ground of predicting for the future, they lead to the fol- 

 lowing conclusions. 



1. When the thermometer rises 25° above the dew point, rain 

 will certainly follow within eight days. 



2. The probability that rain will follow within forty-eight 

 hours is y\. 



3. The probability that it will rain in thirty-six hours is i|. 



4. It is an even chance that it will rain in twenty-four hours. 

 6. It certainly will not rain in less than eight hours. 



Do these facts indicate any necessary connection between ex- 

 treme dryness of the air and subsequent rain ? From the ave- 

 rage of all the observations I have made here, it rains once in 



