ON THE MAGNETIC INTENSITY OF THE EARTH. 4l 
volontiers pendant le petit sejour que je vais y faire, d’y ob- 
server les aiguilles. Ceci me conduit naturellement a vous 
parler des observations d’intensité que vous m’avez vues com- 
mencer a Paris, et que j’ai faites ensuite dans plusieurs lieux 
de l’Inde. Si elles avaient été plus satisfaisantes, je vous en 
aurais entretenu dés mon arrivée; mais malheureusement les 
aiguilles ont perdu pendant le voyage une partie notable de leur 
magnétisme, et M. Arago a été d’avis de ne point s’occuper de 
leurs résultats. C’est ainsi que toutes mes peines ont été per- 
dues, quoique j’eusse eu l’attention de rapporter toutes les ob- 
servations 4 Pondicherry, qui était le centre de nos operations, 
espérant par leur repetition dans le méme lieu, connoitre le de- 
croissement graduel du magnétisme de nos aiguilles. Si je re- 
commence quelque grand voyage, comme je l’espére, je me 
livrerai avec plaisir 4 /’étude de l’intensité, et je m’occuperai a 
Yayance, de faire faire par Gambey l'appareil de plus com- 
mode. Je voudrais connoitre vos idées sur ce sujet.” 
Experience has shown in many cases, and particularly in 
the observations of Capt. King, that it may be possible to ob- 
tain very valuable facts from a series of observations, in which 
the needles have undergene a considerable loss of magnetism 
in the course of a long voyage ; particularly in cases where at- 
tention has been paid to repetition at the same station, for the 
purpose of a frequent examination of the state of the needles ; 
and this was practised by Capt. de Blosseville, as well as by Capt. 
_ King. Aid may also be sometimes obtained from other ob- 
_ servers who may have observed the intensity at some of the 
_ stations: and the publication of a series of determinations de- 
_ pending upon Pondicherry would render it an object with 
persons who might hereafter be engaged in magnetic observa- 
| tions in India, to make Pondicherry one of their stations, and 
thus supply a link to connect M. de Blosseville’s observations 
with Europe. 
| In 1833 Mr. Forbes made a very numerous series of excel- 
_ lent determinations of horizontal] intensity in different parts of 
_ Europe. They were made chiefly with a view to the influence 
_ of height on the magnetic intensity, and are discussed in a 
highly interesting paper in the Edinburgh Transactions for 
_ 1836. The dip was observed with a three-inch circle, at a few 
_ stations only, and Mr. Forbes has nowhere himself deduced 
| the total intensities. If I am rightly informed, he has since 
| made another tour in the same countries, in which magnetic 
_ observations formed a part of his object. We may hope that 
_ by a series of dips, corresponding in extent and exactness to 
his horizontal determinations, he will add greatly to the fulness 
