DISCUSSION OF THE VERTICAL FORCE. 



13 



the process was repeated, if necessary, until all deviations above 30 had been sepa- 

 rated; the final hourly means for each month, thus, found and known as the 

 " normals," are given in the following tables. 



The normals for February, March, April, and May, have been diminished by 198, 

 278, 333, and 361 scale divisions respectively; the uncorrected monthly means are 

 856, 936, 991, and 1019, which can be exactly represented by the expression r 

 966 + 54.4 At 12.8 A< 2 , where r= monthly reading and t, expressed in units of a 

 month, counts from April 1 as the epoch. It shows that the monthly increase is 

 uniformly retarded. The mean reading from the four succeeding months is 658, 

 the corrections to February, March, April, and May, as applied, will produce the 

 same mean. 



The rapid change in the monthly means for some adjacent months makes a small 

 correction necessary to the monthly means, viz : of plus one scale division to the 

 February, March, and December means of the hours 0, 2, and 4, and to the Septem- 

 ber and October means at the hours 18, 20, and 22; of minus one scale division to 

 the February, March, and December means at the hours 18, 20, and 22, and to tLe 

 September and October means at the hours 0, 2, and 4. This small correction is 

 included in the above normals. 



