582 REPORT— 1903. 



uncertainty, as any difference of hours of reading or date of entering is proportion- 

 ally smaller. 



In the special case of charting the annual rainfall of the British Isles for a 

 given year the most serious difficulty is the absence of observations from certain 

 areas ; in charting the mean rainfall the further difficulty is superadded of the un- 

 equal duration of the records. Various methods of overcoming these difficulties 

 are put forward, and maps exhibited showing the distribution of rain-observing 

 stations at work in 1902 in England and Wales, Scotland and Ireland. 



