GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 



49 



to the following scheme, — taking the approximate value at 43% 

 dividing it into four parts, and deriving the final result from 

 five partial results. 



4' 17" 

 28 

 39 

 49 



5 

 11 

 22 

 32 

 43 



4' 38"-5-) 



49 -3 I 

 5 -5 V.O'- 5' O'-l 



10-5 



21 -5 J 



The first column contains the times of notation ; the second 

 the times to which the partial results severally correspond : it is 

 obviously unimportant that the final result, if accurately taken, 

 falls at 0^ 5' 0"-l. If the final result is based on six partial re- 

 sults, then the following scheme is adopted : 



0'' 



4' 12" 

 22 

 33 

 44 

 55 



5 5 

 16 

 27 

 38 

 48 



Oh 



4' 33"-5-| 

 43 -5 

 54 -5 



5 3-5 

 16 -5 

 26 -5 



01' 5' 0" 



The advantage of this modification in the mode of observing is 

 most evident, when it is desired to follow the course of the mag- 

 netic decUnation more closely than at intei-vals of 5 minutes. 

 These intervals, sufficient for the ordinarj^ progress of the changes 

 of declination, are in facttoo large for the examination of the greater 

 and more rapid changes ; and it was in this view, and because 

 shorter intervals coidd scarcely be generally adopted through- 

 out the terms of 24 hours, that subordinate terms were added, 

 each of two hours' duration, in which the observations were 

 to be made at intervals of 3 minutes. As, however, the sub- 

 ordinate terms occasioned some difficulties, and, as they have 

 hitherto brought to light but few phenomena of correspond- 

 ing impoi-tance, it has been decided to discontinue them. The 

 same object can be attained even more effectually in another 

 manner. The rule of obsei-ving at every 5 minutes is retained ; 

 but if at any time rapid changes of declination occur, the obser- 



VOL. II. PART v. D 



