56 PROF. BALFOUR STEWART AND MR. W. DODGSON ON 



(i) Observations at Paris by Cassini, 1784- 1788 ; 



(2) „ „ London, by Gilpin, 1786- 1805; 



(3) „ „ London by Beaufoy, 1 8 13-1820 ; 



(4) „ „ Paris by Arago, 1821-1831 ; 



(5) » » Gottingen, 1834-1840; 



(6) „ „ Munich, 1841-1850; 



(7) » » Prague, 1839-1876; 



4. These observations are recorded as monthly means of 

 diurnal declination-range ; and it is first necessary to mul- 

 tiply each by a certain factor differing for each month of 

 the year, on account of the well-known annual inequality 

 of declination-range. 



This factor is determined for each place by means of the 

 observations taken at that place. For London this factor 

 is taken from the Kew observations. For Paris it is taken 

 from Arago' s observations ; while for Gottingen, Munich, 

 and Prague the factors are taken respectively from the 

 whole body of observations at those places. 



5. In the next place, it is necessary to multiply these 

 observations so corrected by a factor in order to bring 

 them to the Prague standard. We have applied for this 

 purpose precisely the same corrections as those made by 

 Prof. Loomis. They are as follows : — The observations at 



Paris, 1784-88, are diminished by one fifth ; 



London, 1786-1820, „ „ one tenth; 



Paris, 1 82 1-3 1, „ „ one fourth; 



Gottingen, 1834-40, „ „ one fifteenth; 



Munich, 1841-50, „ „ -~ ; 



this last factor has been determined by us. 



6. The compound factor embodying both of these cor- 

 rections is exhibited in the following Table : — 



