IN RAIN AND SNOW, IN THE UNITED STATES. 



143 



future investigatorsi This table is derived from table A, and contains all stations 

 where records extend over one or more years; the resulting mean values given, at 

 the bottom of each column are taken from the monthly mean sums of table A, and 

 will therefore coincide with the means of the annual values of table B, in case the 

 observations suffered no interruption. In order not to lose observations extending 

 over nine or more months in any year, the values for the remaining months were 

 interpolated, either by substituting the average values at those months, as resulting 

 from the whole series, or by substituting, when practicable, amounts observed at an 

 adjacent station. Such interpolated annual amounts have less weight, and are dis- 

 tinguished by an asterisk ; they may be omitted, if desirable, in rigorous investiga- 

 tions. The fact that comparatively few of the records, extending over a number of 

 years, at any station, are free from occasional interruptions, greatly increases the 

 labor of reduction, and seriously interferes with the value of the whole record. 

 The difficulty in attempting to interpolate any monthly amount, even within the 

 limits of a city, will appear in the following sample of comparisons of annual 

 amounts, as given by three observers at different stations in San Francisco: — 



1853- 



By Assist. Surg. U. S. A. . 

 " Mr. Walthall and Dr. Gibbons 









18.70 inches. 

 19.70 " 



1854. 



" Assist. Surg. U. S. A. . 



" Mr. Walthall and Dr. Gibbons 









17.00 " 

 22.12 " 



1855- 



" Assist. Surg. U.S. A. . 









19.26 " 

 26.39 " 



1856. 



" Assist. Surg. U.S.A. . 









14.40 " 

 22.31 " 



1857- 



By Assist. Surg. U. S. A. . 

 " Mr. Tennent 









16.04 inches. 

 12.97 " 



1858. 



" Assist. Surg. U. S. A. . 



" Dr. Ayres .... 









15-95 " 

 17.76 " 



1859. 



" Assist. Surg. U. S. A. . 









16.34 " 

 21.39 " 



i860. 



" Assist. Surg. U.S. A. . 









20.19 " 



From these comparisons the great diversity in the corresponding monthly amounts 

 may be inferred. Quite a remarkable case of an extraordinary fall of rain, which 

 occurred at Charleston, S. C, in August, 1859, with a sharply defined boundary, is 

 recorded in the statistical report on the sickness and mortality in the army of the 

 United States, between 1855 and 1860, by Brevet Brigadier-General T. Lawson, 

 page 504. " If two inches could fall during one and half an hour in one part of 

 the city (at the U. S. Arsenal), while but 0.35 fell at the same time about two 

 miles distant (City Kegistrar, Tradd Street), it may be readily believed that even 

 if only six and three-quarter inches fell in Charleston during thirty hours, 16.45 

 inches, or even twice that quantity, may have fallen in forty-seven and one-half 

 hours at Sullivan's Island, which is seven miles distant." 



If the rain-fall is recorded by more than one observer in any place, for the same 

 month or year, the mean has been taken and inserted in Table B. 



