ON THE MAGNETIC SURVEY OF ENGLAND. 



267 



where A is a constant obtained by the formula 



. X /sin u si 



COS^v/ COSi 



smu. 



from observations made at a base station where X and have been carefully 

 determined. 



The Observatory at Kew having been taken as a base station, the experi- 

 ments detailed in Tables IX. and X. were kindly made at my request by 

 Messrs. Stewart and Chambers in January 1859 and October 1860, to de- 

 termine the value of the constant A at those epochs. 



Table IX. — Observations made at the Kew Observatory by Mr. Chambers 

 in January 1859, with needles 3 and 4 of Circle 30, to determine the value 

 of the constant A. 



X= 10-290 (Tables V. & VI.). 0=68° 22' 18" (Proceedings of the Royal 



Society, vol. xi. p. 151). 



Table X. — Observations made at the Kew Observatory by Mr. Stewart in 

 October 1860, with needles 3 and 4 of Circle 30, to determine the value of 

 the constant A. 



X=10-290 (Tables V. & VI.). Q=6S° 19'-6 (Proceedings of the Royal 



Society, vol. xi. p. 154). 



It appears, therefore, that the constant A was substantially the same at an 

 early stage and at the close of the survey experiments. The value employed 



has been A= log 0-87516. 



Table XI. exhibits the results of the statical determination of the Total 

 Force at the stations of the survey where that method was employed. 



