458 



KXI'KDITION TO POINT BARROW, ALASKA. 



Talilr nf i-<:<it!lini/ iHiitinrtic tle 

 (Values ii'dueed to mean nl' liiulllli by mi "I I lie dilleienl i;il ol.-el vat mils 1 



The following results, except the first, are those mentioned as affected by torsion; some of these 

 we propose to use differentially they are all reduced to the mean of .the month respectively : 



' New pnsitiuii of iustrument ami a new immutb useil Here. 

 t'J'orsion partly removed by observer. 



oliserver attempted to take nut ihe t'usion. After tbia date the i 

 snspended on two iil>er. 



^as .su.s)teixled tin a single tib"i ; it h:nl j 



i: . 



Toward the middle of August, 188-', the deflecting force of torsion had become constant and 

 remained so till the middle of February the following year. For this period we have the follow 

 ing means and the corresponding monthly means of the readings and of the Brooke differential 

 magnetometer ; the mean correction to the absolute results is then found as shown below . 



Menu 



+ 5 34.0 



The two values within parentheses in column headed > are interpolated : 3lean leading of decli- 

 nometer for the last ."> months, 47(i''.2, and for the preceding 5 months. 4.S.S''.4. hence difference lor ~t 

 months. 1 li' 1 . 1', or monthly change, 2'.4, and the first interpolated value becomes 4 x L'.l + 4SS.4 = I'.tS.d 

 The lit'tli cohmin gives the computed 'declination corresponding to difference / r. or for the reading 

 r, and the torsion correction is determined by the difference /> I'.. Our completed series, when 

 compared with the preceding series (March to August. 1*s:; . exhibits necessarily a trace of the 

 comparatively rapid monthly decrease in the differential series between February. 1<SS.'J (mean 180.5) 

 and May, 188.'! (mean ITli.1 ). but the magnitude oft lie errors of observation of the absolute measures 

 forbids any attempt at correction of the differential series. Omitting the value for August. 1SS2, 

 \ve limilly have the table of absolute values, as follows: 



