16 



DISCUSSION OF THE VERTICAL FORCE. 



The normals for 1843-44 at the even hours are complete, at the odd hours they 

 extend only over nine months. To refer the latter to twelve months, the difference 

 between the means of the same nine months and the annual mean at the even hours 

 was made out and applied as a correction to the means of the odd hours ; the cor- 

 rection thus applied is the mean difference as deduced from the preceding and fol- 

 lowing even hour. 



