520 
MR. A. W. RUCKER AKD DR. T. E THORPE ON A MAGNETIC 
In the next Table we compare the Dips at the Central Stations, with the 
calculated values obtained from Table IX. 
Dips at Central Stations. 
District. 
Mean value observed 
in district. 
Calculated. 
Difference. 
T. 
70 57-3 
70 58-0 
- o'7 
11. 
70 9-3 
70 11-3 
- 20 
lit. 
68 53'6 
68 53'6 
00 
IV. 
67 42-2 
67 43-5 
- 1-3 
V. 
69 o2‘6 
69 51-9 
+ 0-7 
VI. 
69 19'5 
69 20-2 
- 0-7 
VII. 
67 32-1 
67 32 8 
- 0-7 
VIII. 
69 11-9 
69 144 
— 2"2 
IX. 
68 5-2 
68 6'7 
— lo 
The differences here are for the most part negative, and, in accord with this, 
the Table on p. 521 shows that the calculated isoclinals, on the whole, run a little 
below the district curves. 
A_ better result would be obtained for the central stations if a formula were adopted 
which diminished the calculated Dips by 0'’9. Inasmuch as, on the average, the Dip 
alters by 1° for a change of 1° 40' in latitude, this would move the isoclinals 
0'9 X lOO/GO = 1*5 minutes of latitude further north. This, however, would place 
them as much to the north of the district lines as they are now to the south of 
them, and would make the discontinuity in the North of Scotland more conspicuous. 
On the whole the formula seems to give as good a representation of the facts as the 
inherent difficulties of the case will allow. 
In the Table on p. 521 we give the data required in order to draw the isoclinals 
deduced from Tables VIII. and IX. respectively. 
The lower number in each square is, as before, that given by the district curve, 
and the upper is that calculated from the formula by the aid of Table IX. 
TI .e curves themselves are exhibited in Map 3. The district curves are dotted, 
the terrestrial curves are drawn in continuous red lines. 
