LIEUT. -COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
119 
the Seychelles and all preceding 1 stations : or if the ratio of the intensity is sought be- 
tween those stations and one visited subsequently to Madagascar, — (as for example 
Woolwich, where the observations with No. 5. were made in December 1842), — 9-9857 
must be subtracted from, or its arith. comp. 0*0143 added to, the squares of the times 
of vibration at the earlier stations. 
Differences of the logarithms of the squares of the time of vibration of No. 5. with 
those of Nos. 9. 11. 12. and 13. 
Stations. 
No. 9. 
No. 11. 
No. 12. 
No. 13. 
Preceding 
the loss ; 
f Penang 
9-9401 
0-0049 
9-8674 
9-8470 
1 Point de Galle .... 
9-9406 
0-0036 
9-8678 
9-8458 
( Seychelles 
9-9408 
0-0041 
9-8680 
9-8481 
Mean (a) .... 
9-9405 
0-0042 
9-8677 
9-8476 
Following 
the loss ; 
f Madagascar 
9-9265 
9-9901 
9-8530 
9-8331 
1 Cape of Good Hope . 
9-9261 
9-9885 
9-8530 
9-8315 
( Ascension 
9-9256 
9-9918 
9-8538 
9-8341 
Mean ( b ) .... 
9-9261 
9-9901 
9-8533 
9-8329 
(b) - (a) = 
9-9856 
9-9859 
9-9856 
9-9859 
By a similar comparison, of which the particulars are also subjoined, No. 7- is 
shown to require a correction of 9‘9885 to be added to the logarithms of the squares 
of the times of vibration at Madagascar and the subsequent stations, or of 0-0115 to 
be added to the logarithms at the stations antecedent to Madagascar, to render the 
series of observations with this needle before and after the loss thus ascertained com- 
parable with each other. 
Differences of the logarithms of the squares of the times of vibration of No. 7- with 
those of Nos. 9. 11 . 12. and 13. 
Stations. 
No. 9. 
No. 11. 
No. 12. 
No. 13. 
Preceding- f Penan S 
preceding I Point de Galle 
[_ Seychelles 
Mean (a) .... 
rn . f Madagascar 
the°loss •* i ^ a P e °f Good Hope . 
’ (Ascension 
Mean (b) .... 
9-8232 
9-8217 
9-8224 
9-8880 
9-8847 
9-8857 
9*7505 
9-7489 
9-7496 
9-7301 
9-7269 
9-7297 
9-8224 
9-8861 
9-7497 
9-7289 
9-8100 
9-8120 
9-8103 
9-8736 
9-8744 
9-8765 
9-7373 
9-7389 
9-7377 
9-7166 
9-7174 
9-7188 
9-8108 
9-8748 
9-7380 
9-7176 
(b) - (a) = 
9-9884 
9-9887 
9-9883 
9-9887 
The loss of magnetism thus manifested in Nos. 5. and 7- at the Seychelles is the 
most considerable change undergone by any of the needles between March 1839 and 
December 1842. The only change of nearly equal amount (being also a loss for 
