48 
THE KEY. STEPHEN J. PERRY ON THE MAGNETIC 
of reduction. A comparison of these maps with those of the latest surveys of the British 
Islands manifests a striking resemblance between the isoclinal lines in France and 
England. For in the Report by General Sabine for the British Association 1861, we 
find that the direction of the isoclinals in England was —65° 5' in 1837, and — 71° 22' in 
1860; therefore, supposing the rate of change to remain constant, we have — 73° 33'-2 
as the value for 1868, —73° 25' ‘2 being the amount found for France in August and 
September of the same year. The values of r, 0-678 and 0-644, show, however, that the 
lines are closer packed in France than in England, and this is confirmed by the observa- 
tions taken with needle No. 1 at Kew and at Stonyhurst immediately after our return 
from France ; for if the angles be computed on the assumption of the same data holding 
in England as in France, we shall have : 
Kew . 
Stonyhurst . 
Observed. 
68- 087 
69- 707 
Computed. 
Difference. 
68-241 - 9-24 
70-306 -35-94 
The isogonics of France are nearly in the same direction as those of Scotland, as seen 
in Dr. Stewart’s Report of Mr. Welsh’s Survey ; but they are nearly twice as close in 
Scotland as in France, the values of r being 0'-677 in 1868 for the latter country, and 
l'-465 for the former in 1858. 
The greatest difference is in the isodynamics, their angle for England being — 58° 32'-7, 
andr=0 - 00106, whilst for France at the same epoch, 1868, the values are —70° 34' 13"T 
and 0-00087. 
The following is a complete Table of all the elements at the Epoch Jan. 1st, 1869. 
Table XVI. 
Station. 
Dip. 
Declination. 
Horizontal Force. 
Abbadia 
62 27-8 
18 1410 
4-5456 
Amiens 
66 40-3 
18 1896 
40143 
Angers 
65 8-4 
19 5 58 
4-2106 
Bayonne 
62 30-2 
18 23-46 
4-5520 
Bordeaux . 
63 23 0 
18 12-54 
4-4110 
' Eourges 
64 32-6 
17 0-18 
4-2845 
Brest 
66 26-4 
21 0-30 
4 0442 
Laval 
65 48 1 
19 4-38 
4 1245 
Paris 
65 52-5 
17 50 46 
41133 
Pau 
61 58-2 
17 49-50 
4-5823 
Perigueux 
63 23-9 
17 40-92 
4-4268 
Poitiers 
64 28 1 
18 18-36 
4-2955 
Toulouse 
62 1-1 
17 7-32 
4-5883 
Vannes 
65 47 1 
20 13-50 
41328 
Annual Variation 
-3-68 
-9-1 
+0 0050 
Acceleration 
0043 
0-19 
0-00002 
In none of the previous reductions have I ventured to introduce a correction for any 
magnetic disturbance that might have existed at the time of observation, or for diurnal 
range, since there were no self-recording magnetographs in France by which these cor- 
