Chase.] 



526 



[1868. 



slight as to be easil}^ overcome, and sometimes for five or more 

 coiisecu-tive years, and for periods of ten years or more, this law 

 of precipitation appears to be entirely reversed. Some indica- 

 tions of a probable cause for this vacillation appeared to be 

 furnished by the barometric octantal tides which I had previously 

 pointed out {ante IX., 398 ; Proc. Ro3^ Soc. June IC, 1864), 

 and these indications were strengthened by Mr. Hennessey's 

 report of the observations at Mussoorie, which showed not only 

 a greater rainfall at each quadrature than at either syzygy, but 

 also a general octantal maximum. 



TABLE V. 



Philadelphia Rainfall and Barometric Means on different days 

 of the Lunar Month. 



I was therefore led to plot and compare the pluvial and baro- 

 metric curves, smootliing the irregularities by Airy's method. 

 The normal ordinates (r-) were each derived from seven succes- 

 sive observations {y) hy the formula '';«= 



{l/n-Z + 6^n-2+ 1 ^Un-l + ^O^, + 1 5^, , ^ + G^^.o + 1/ „ . ,) -64 



