42 



EXPEDITION TO POINT i'.AUKOW, ALASKA. 



From evidence similar to that given for the dip, but less conclusive, it is probable that // is on 



increase, though the above amount appears far too large. In the discussion of Captain 



Maguire's observations at Harrow Point in 1852-'53--'54, Sir Edward Sabine assumes // for that epoch 



about 1.70 Tliis value when compared with the above would indicate an annual increase of about 



+0.608 



Second and independent determination of the hori/ontal force by means of the Kew Dip 

 Circle, according to Doctor Lloyd's method* of deflections by gravity and by magnetism in con- 

 junction with dip observations. This method has the great advantage of being independent of the 

 temperature and of any loss of magnetism of the needle, and applies well for stations in high 

 magnetic latitude. 



The monthly observations for intensity witli the Dip Circle at TJglaamie commence in June, 

 LSSi'. and terminate with August, 1883. Washington, D. C., was selected as a base station, and 

 the value of the constant A H sec ^Vsiii w o sin ' sec r /0 became known from the observations 

 of Sergeant Maxneld, in January and February, 1884. AVe have for the deflecting weight employed 

 at Uglaamie previous to September, 1882, the values: 



r, =4l 04'. 4 from 12 sets of observations. Lloyd's needle JTo. 4 weighted: February 15, 



1884. 

 =70 39'. 4 from annual observations for 18 years, 1807 to 1884. reduced to Fcbruai v, 



1884. 



1/0= 2'. i- :;.v.( i 



H' =37 19'.! from 12 sets of observations, Lloyd's needle No. 4, deflecting No. ">, Feb- 

 ruary 15, 1884. 



Hence log A 0.92055. using .H =4.378, as deduced from annual observations for 18 years, 1807 to 

 1884, reduced to February, 1884. 



For the deflecting weight employed at Uglaamie after August 23, we have 



r, =4l 34'.G from 7 sets of observations, Lloyd's needle No. 4 weighted; January 30, 31, 



February 1, 2, 1884. 



= 70 37'.3 from 10 sets of observations, dip circle No. 23. 

 ?(o=29 02'.7 

 ' u =. ,7"l(i'.o from 7 sets of observations, Lloyd's needle No. 4, deflecting No. 3; date 33 



above. 

 Hence, log A=0.9175!> 



The results at Uglaamie are then worked out by the formula 



HA cos #\/cos i; cosec K cosec n' 



which were tabulated as follows : 



Table of resulting values for magnetic horizontal force (H) at Uglaamie, as determined by 

 Kew Dip Circle No. 23, from gravity and magnetic deflections: 



"Mean horizontal component of magnetic intensity from 15 months of observations, J.',I35 (English 

 units), for the epoch January (middle), 1883, with apparently an annual diminution. 



* Directions for iiicaMiivuiiMit !' torrrat rial inaguotitiin. C'o:il anil (icodctir Suivi'.v Ki'jiorl lor 1-v-q, 

 Ko. 8, p. 145, Art. (10). 



