ON THE MAGNETIC SURVEY OF SCOTLAND. 



169 



It appears from this Table, that, while the mean of all the circles gives a dip 

 of 68° 22'-5, the observations with circle No. 23 give 68° 23'5, or 1' higher. 



This difference is so small, that it has been thought unnecessary to apply 

 any constant correction to the dips on account of it. It is therefore pre- 

 sumed that circle No. 23 is calculated to exhibit the true dip at the place of 

 observation. 



An equal weight has been attached to each of the mean dips obtained at 

 the various stations, without regard to the number of observations made at 

 any station, in accordance with a remark of General Sabine, that an ab- 

 normal result is more likely to be due to local magnetism than to error in 

 observing. 



The dips have been corrected for secular change to the epoch of 1st 

 January, 1858. The yearly rate of change has been ascertained by com- 

 paring the observations of the present with those of the previous survey. 

 The method is exhibited in the following Table : — 



Table III. 



Station. 



First Dip. 



Date of 

 First Dip. 



Lerwick.., 



Aberdeen 



Kirkwall 



"Wick 



Golspie .. 



Inverness 



Fort Augustus 



Berwick 



Melrose 



Alford .... 

 Gretna .... 

 Edinburgh. 



Glasgow i 



Helensburgh 



Campbelton , 

 Cumbray .... 



73 



72 



73 



73 



72 



73 



72 



72 



72 



71 



71 



71 



72 



71 



71 



71 



72 



72 



72 



72 



71 



72 



44-9 

 27-6 

 20-4 

 19-9 

 55-5 



4-3 

 4G-4 

 46-2 

 40-3 

 41-9 

 36-8 

 38-0 

 21-9 

 29-0 

 50-3 

 50-0 



1-6 



50 

 16-7 

 17-0 

 55-9 



11 



Second 

 Dip. 



1838 



1838 



1838 



1838 



1836 



1838 



1836 



1838 



1836 



1838 



1836 



1837 



1836 



1837 



1836 



1837 



1836 



1837 



1836 



1838 



1836 



1836 



11-9 



49-3 



40-9 



39-5 



25-0 



25-0 



7-9 



7-9 



2-6 



54-8 



54-7 



70 54-7 



71 45-9 

 46-0 

 11-2 

 12-5 

 263 

 263 

 29-6 

 29-6 

 140 

 28-9 



73 

 71 



72 

 72 

 72 

 72 

 72 

 72 

 72 

 70 

 70 



70 

 71 

 71 

 71 

 71 

 71 

 71 

 71 

 71 



Date of 



Second 



Dip. 



1858 



1857 



1858 



1858 



1858 



1858 



1857 



1857 



1857 



1857 



1857 



1857 



1857 



1857 



1857 



1858 



1857 



1857 



1857 



1857 



1857 



1857 



Difference 

 of Dips. 



Difference of 

 dates in years. 



330 

 38-3 

 395 

 404 

 30-5 

 39-3 

 38-5 

 38-3 

 377 

 47-1 

 42-1 

 433 

 360 

 430 

 39-1 

 375 

 353 

 38-7 

 47-1 

 474 

 41-9 

 322 



20 

 19 

 20 

 20 

 22 

 20 

 21 

 19 

 21 

 19 

 21 

 20 

 21 

 20 

 21 

 21 

 21 

 20 

 21 

 19 

 21 

 21 



Yearly rate 

 of decrease. 



1-65 

 2-02 

 1-97 

 2-02 

 1-39 

 1-96 

 1-83 

 201 

 1-80 

 2-48 

 2-00 

 2-16 

 1-71 

 2-15 

 1-86 

 1-79 

 1-68 

 1-93 

 2-24 

 249 

 1-99 

 1-53 



Mean annual rate of decrease =T94 



In reducing the dips to the epoch, a yearly rate of decrease of l'-94, or 

 in round numbers 2', has accordingly been adopted. No other correction 

 has been applied to the observations. They are thus presented to our view 

 in the following Table : — 



