518 Annual Report of the New York "Weatpier Bureau. 



For a 15 years' record' the probable error of moutlily means 

 =10 per cent. 



For a 10 years' record the pr.obable error of monthly means 

 =12 ppr cent. 



As stated, these values are but rough approximations, since 

 the departures from rainfall averages do not fully meet the defi- 

 nition of residuals as employed in the meithod of least squares. 



All records under ten years in length were corrected for the 

 general excess or deficiency of rainfall during their period by 

 comparison with the nearest station having an established nor- 

 mal, no correction being attempted, as a rule, for longer series. 

 A few four and five j-ears' averages have been admitted when 

 longer records were lacking, in case the deviation from neighbor- 

 ing stations was of a somewhat constant character, as, for ex- 

 ample, in comparing the rainfall of the Adirondack plateau with 

 that of the Champlain valley, an excess in the rainfall of the 

 former over the latter region was almost uniformly noted in the 

 case of individual months. 



