16 
THE REV. STEPHEN J. PERRY ON THE MAGNETIC 
Table VIII. 
Station. 
Computed H. P. 
Observed H. F. 
Obs. — Comp. 
Paris 
4-1259 
4-1182 
-0-0067 
Rheims 
4-1121 
4-1198 
+ 0-0077 
Metz 
4-1548 
4-1570 
+ 0-0022 
Strasburg — 
4-2282 
4-2531 
+ 0-0249 
Issenheim 
4-2732 
4-2743 
+ 0 0011 
Mont Rollantl... 
4-3268 
4-3325 
+ 0-0057 
Dole 
4-3310 
4-3231 
-0-0079 
Dijon 
4-3044 
4-2974 
-0-0070 
Lyons 
4-4429 
4-4488 
+ 0-0059 
Avignon 
4-6084 
4-6254 
+ 0-0170 
Marseilles 
4-6771 
4-7238 
+ 0-0467 
Monaco 
4-6699 
4-6602 
-0-0097 
Montpellier 
4-6254 
4-6389 
+ 0-0135 
Grenoble 
4-5101 
4-4348 
-0-0753 
N. D. de Myans 
4-4847 
4-4847 
0-0000 
Mongre 
4-4213 
4-4143 
-0-0070 
St. Etienne 
4-4669 
4-4641 
-0-0028 
Clermont 
4-4150 
4-4044 
-0-0106 
Moulins 
4-3477 
4-3387 
-0-0090 
Douay 
3-9969 
3-9964 
-0-0005 
Boulogne 
3-9434 
3-9491 
+ 0-0057 
Excluding Paris, which does not enter as a station into our equations of condition, we 
obtain for the probable error of the mean value of the observed H. F. at any single 
station 
0-6745 ^/ U ' (JO ^^ 6 j32 = + 0 - 01513 , 
whilst the error of the computed value for the central station will be ±0-00338. 
It remains for us to deduce the secular variation of the Horizontal Force from the 
observations taken at those stations which are common to the two surveys of 1858 and 
1869. 
Table IX. 
Station. 
H. F., Jan. 1, 
1858. 
H. F., Sept. 1, 
1869. 
Diff. of Epoch. 
Diff. of H. F. 
Yearly rate of 
increase. 
IL. F., Jan. 1, 
1869. 
Clermont 
4-3523 
4-4044 
Hf 
+ 0-0521 
+ -00447 
4-4013 
Dijon 
4-2385 
4-2974 
+ 0-0589 
+ •00505 
4-2943 
Marseilles 
4-6332 
4-7238 
>9 
+ 0-0906 
+ -00777 
4-7207 
Montpellier 
4-5788 
4-6389 
+ 0-0601 
+ •00515 
4-6358 
Moulins 
4-2871 
4-3387 
+ 0-0516 
+ -00442 
4-3356 
Paris 
4-0685 
4-1182 
5? 
+ 0-0497 
+ •00426 
4-1151 
Mean (omitting Marseilles) 
+ •00467 
The yearly rate deduced from the observations of 1858 and 1868 in the west of France 
was -j- 000507 ; hence the rate of increase appears to be slower in the east than in the 
west, whilst the mean rate for the whole of France is identical with that given by 
Hr. Lamont for 1858, the yearly acceleration being less than 0-000007. 
