140 TABLES AND RESULTS OF THE PRECIPITATION, 



to have been the practice, at some stations, to divide the sum of rainy hours by 24, 

 to obtain the number of rainy days; it is often doubtful whether a bar — is to be 

 interpreted "no record," or "no precipitation." Secondly, it was thought unneces- 

 sary to develop separately the laws to which the number of rainy days appear 

 subject, since they are nearly identical with those of the amount, and generally but 

 slightly depending upon the seasons. In my discussion of the rain-fall at Marietta, 1 

 Ohio, it is shown that the copiousness of precipitation is nearly the same throughout 

 the year. The following table gives, for each month, the average quantity in any 

 one day, as derived from thirty-two years of record. 



Month. 



No. of rainy 



Average fall of rain 





days. 



(or snow). 



January, 



6.1 



0. 44 inches. 



February, 



5-9 



•5 1 ' 





March, 



6.7 



• 44 ' 





April, 



7-5 



.44 ' 





May, 



8.4 



•5° ' 





June, 



9.2 



•Si ' 





July, 



8-3 



•53 ' 





August, 



7.6 



•53 ' 





September, 



6.2 



•5 2 ' 





October, 



6.8 



.48 < 





November, 



6.4 



•5 2 ' 





December, 



6-5 



•55 ' 





Dividing the average monthly amount by the average monthly number of rainy 

 days, the quotient is nearly the same for the extreme sections; the summer rains 

 are slightly heavier than the winter rains. The same is the case at Brunswick, 2 Me., 

 as shown by the following table of daily averages (of rain and snow) copied from 

 my discussion and derived from thirty-two years of record. 



January . 



• o-33 



July . . 



• -5i 



February 



• -34 



August . 



• .65 



March 



.42 



September 



• -5i 



April 



. .46 



October . 



• -54 



May 



• -5i 



November 



• -55 



June 



• -5i 



December 



.42 



The heaviest rains therefore fall in August, the lightest in January and February, 

 epochs in which the air's capacity for vapor is greatest and least, respectively. 



The following figures are copied from Tables IX and X of Prof. Caswell's Meteo- 

 rological Summaries, 3 for Providence, R. I., to which I have added the ratios in the 

 last column, derived from twenty-eight years of observation. 



1 Results of Meteorological Observations made at Marietta, Ohio, between 1817 and 1859, by J. 

 Wood and Dr. S. P. Hildreth. Smithsonian Contributions to Knowledge, No. 120. Washington, i 

 1868. 



2 Results of Meteorological Observations made at Brunswick, Me., between 1807 and 1859, by 

 Prof. P. Cleaveland. Smithsonian Contributions to Knowledge, No. 204. Washington, 1867. 



3 Meteorological Observations made at Providence, R. I., between 1831 and 1860, by Prof. A. 

 Caswell. Smithsonian Contributions to Knowledge. Washington, 1860. 



