Considerations on the Problem of Latitude Variation. 27 



to the mean would consequently need a corresponding revision. 

 Thus in order to find liow the above corrections enter into tlie re- 

 duction by chain method, i. e. , how to reduce them to a true 

 homogeneous system, we must treat these corrections in a manner 

 exactly identical with the chain method reductions. 

 I form, tlierefore, — 



Correction to III-IV = Difference of corrections to Ills & IVi = +o!bl 



IV-V = „ IV2 & Vi = +0.02 



V-VI = „ v. & VI, = +0.02 



VI-VII = „ VI2 & VIIi = +0.02 



VII- VIII = „ VII2 & VIII, = +0.01 



VIII-IX = „ VIIIo & IX, = +0.01 



IX-X = „ 1X2 & X, = +0.01 



X-XI = „ X2 & XI, = +0.01 



XI-XII = „ XT2 & XII, = +0.02 



XII-I = „ XII2 & Il = +0.02 



I-II = „ I2 & III = +0.02 



II-III = „ II2 & III, = +0.01 



Hence, 



the correction to the closing sum, in the usual sense, = +0.18 



Further, in order to find the corrections to the reductions to 

 the mean system, I form, — 



for the gi'oup III ; correction to 



I apply similar treatment to the other groups and divide the 

 sums by 12. 



