MADE AT MARIETTA, OHIO. 41 



The average annual amount of rain (a,nd melted snow) from 38 years of observa- 

 tion is 42.56 inches; the least quantity observed in any one year 32.46 inches (in 

 1866); and the greatest quantity 61.84 (in 1858). These extreme variations are 

 much less than those recorded at Brunswick, Me., although the latter series of 

 observations extends over 32 years only. 



455 2A^ 



The probable uncertainty of the above annual mean is ^ — — — = ±0.7 inches. 



■^ n (n — 1) 



The last two columns of Table XI contain the annual variation in the amount 

 of precipitation ; the monthly means are derived from 38 years (that of October 

 from 37 years), and the diiference from the average amount, 3.55 inches, is shown in 

 the last column ; the + sign "in the months of May, June, July, and August indi- 

 cating more than the average amount, and the — sign in the remaining months 

 less than the. average. In the annual fluctuation there is but one well-marked 

 maximum of rain in June (corresponding to that of May at Brmiswick, Me.), and 

 one well-marked minimum of rain (and snow) in January (corresponding to that of 

 February at Brunswick, Me.). 



Table XI (6) contains the number of days of precipitation, or the frequency of 

 rain (or snow) ; the column of monthly means is derived from 32 years (on the 

 average), and plainly indicates an annual fluctuation which is better shoAvn in the 

 'last column headed "difference from annual mean" (7.1 days). In February rain 

 or snow falls on one day less, and in June rain falls on two days more than on the 

 average in any one month. The average number of rainy days in the year is 86 

 nearly, varying between 44 and 113. 



If we divide the monthly mean amoimt by the average monthly frequency, we 

 obtain the average quantity of rain in any one day. 



Average Quantity in any one Day of Rain (or Snow). 



January 0i".44 



February ...... 0.51 



March 0.44 



April . ■ 0.44 



May 0.50 



June ...... 0.51 



July 0".53 



August 0.53 



September 0.52 



October 0.48 



November 0.52 



December 0.55 



The copiousness of precipitation is nearly the same throughout the year; in 

 summer the rains are slightly heavier than in winter. The Brunswick series of 

 observations in this respect was far more decided in its results. 



On the average a fall of rain, on any day, amounts to 0.50 inches; while at 

 Brunswick the quantity was 0.48 inches. The three heaviest falls of rain recorded 

 on any one day were October 22, 1858, 3.1 inches; December 10, 1847, 3.5 inches; 

 and Jidy 3, 1844, 4.25 inches. Very heavy (comparatively) falls of rain may there- 

 fore take place in midwinter as well as in midsummer. 



Snow. 



Snow is recorded to have fallen as late as May 13 (in 1829), and as early as 

 October 4 (in 1836). The heaviest faU of snow occurred February 1, 1830, when 

 7 inches fell; April 18, 1854, 8 inches; January 14, 1831, and again December 

 14, 1833, 15 inches; even as late as April 29 (in 1854), as much as 4 inches fell. 



August, 1867. 



