460 



EXPEDITION TO POINT BABftOWj ALASKA. 



1. Table f rrHitltiny tlifi <it t'yltiamic. 





M.-ans SI 23.4 



Mean dip from twenty months of observation, 81 23' A, answering to the epoch October], 

 si'. Annual diminution of the dip, 1'.- 



Applying the efl'ect of the secular variation, or, uiorc properly, of the annual chauge to the mean 

 monthly values, i. e. to i (#1 + ^11) for the months from December to July, inclusive, and to ^, the 

 correction O'.G for the months of August, September, October, and November, we obtain the 

 following table of monthly dip values, all reduced to the same epoch, and which, therefore, should 

 indicate any annual variation that may exist, unless in consequence of the smajlness of such vari- 

 ation it be hidden by the observing errors: 



2. Table of -mean monthly dipa reduced to the mine e/ioclt (December, 1882). 



1 '.iii ini'Iilli <>f 



IS -i i mlier. 1RK1 anil ls'-' 

 January, 1SK2 and is-:; 

 February, 1882 and ISKJ 

 Marrh. 1882 and is>:: 



April, ISKJnnil lss:i 

 ilav, ish^ainl 1 .->:: 

 Julie, 1882 and lss:t 

 July, 1882 and l>s; 

 AiiK s t. 1SS1' li uiiiullis 

 Seiiti-inbvr, 1SS2 I! month* 

 Outolier. 1SSJ i; months 

 \o\ finhi'i, 18s" fij inontlis 



M,. 

 i an iuj>. 



Cm rortiim for 

 i 



If the results exhibited in the last column of the table can be trusted for such small ditt'erem-es 

 from the mean (81 a 23'.l), they would indicate a slightly greater dip about the time of the vernal 

 equinox and a slightly smaller dip about the time of the autumnal equinox. 



The probable uncertainty of a monthly determination of the dip, /'. r.. of any one of the values 



H t or ti n is found to bo "." = J- 1'.4 about. 

 v 3 



Observations at NVasliington, D. 0.; at Toronto, Canada: at .Madison. Wis.: at lOsquinrault, 

 British Columbia; at Sitka, Alaska, and at many intermediate places (see preface to '-Diary of a 

 magnetic survey of a portion of the Dominion of Canada," by General Sir J. H. I.efroy. London, 

 iss;;; show that the dip as well as the total intensity of the magnetic force are at the present time 

 anil have been for some years past slowly ili'n-c'iniiiji, and our result at TTglaamie is conformable 

 with this general and extended action of the secular change. (Jeneral Lefroy also slates that at 

 Fort Ifae. (Ireai Slave Lake, the present rate of the secular variation is I/. 7 per annum, deter- 

 mined from comparisons of observations liy Capt. II. P. Dawson, with an earlier deduction. Both 

 at Washington and Toronto the dip reached a maximum in 18.1!), at which time it is nearly certain 

 that the total force had been declining for some years. In 18.").'!, Captain -Maguire. K. N., found the 

 dip at Plover Point, about 2.h miles southeast of Barrow Point, 81 .'50' (Phil. Trans. Koy. Soc'y, 

 Is.iT, vol. 147, Part II, London, 1.S5S). indicating an apparent diminution of \'.V in i'<) years, but it, 

 is highly probable that since Captain Maguire's occupation of this point the dip was on the increase 

 for a few years In-fore its present reversed motion commenced. 



