'^1 ^ 



1S70.] u L'J [Chase. 



II. Monthly Normals of Rainfall at Philadelphia, for 40 Years. 



Table I. indicates the following probabilities: 



1. Of a change of weather (from a preceding wet month, or season, to 

 a dry one, or vice versa). 



In September, f In Autumn, -^-^ 



" November, f 



" January, y\- 



" April, j% 



2. Of a continuance of the weather of the pi-eceding mouth or season. 

 In January, f In Winter, -^^ 



" February, yt " Summer, -| 



" October, yV " Spring, -^-^ 



" December, -^-^ 



The indicated probability, nearly f , that a rainy February will be fol- 

 lowed by a dry Summer (June to October, inclusive), and vice versa, is 

 very curious. 



