ON THE MAGNETIC INTENSITY OF THE EARTH. 85 
Estcourt, 1836.—These observations were made during the 
late survey of the navigation of the River Euphrates, conducted 
by Colonel Chesney. 'The magnetic observations were entrusted 
to Major Estcourt, who was furnished with a good dip circle 
by Robirison, and an apparatus similar to M. Hansteen’s, with 
eight horizontal needles: Numerous observations were made 
with these at Port William and Bussora, the manuscripts of 
which have been sent to me, by the President of the Board of 
Control, to arrange for publication in the official account of the 
proceedings of the expedition, preparing under the direction of 
Colonel Chesney. On the arrival in England of the needles, 
which only took place very recently, they were also placed in my 
hands, in order that the necessary comparative observations 
might be made with them. It had unfortunately happened that 
the manuscript containing the times of vibration of the needles 
observed by the officers of the expedition before its departure 
from England, were on board the Tigris steamer when she 
was lost in the Euphrates, and no record was preserved. But 
- on receiving the needles, I recognised two of the number as 
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having belonged to Professor Lloyd, of Dublin, and as having 
been employed by Mr. Lloyd and myself in Ireland. I had 
consequently a memorandum of their rates before they were 
given to the officers of the expedition; and on vibrating them 
in Sussex, where I was staying when I received them, I per- 
ceived with great satisfaction that these two needles must have 
preserved their magnetism wholly or very nearly unaltered. 
‘They were immediately sent to Professor Lloyd, who kindly 
vibrated them at the same spot in which they had been used in 
1834, and found their magnetism almost identical with what it 
had been at that period. On trying the six other needles, I 
found that two gave similar values for the intensity at Port 
William and Bussora with those of Mr. Lloyd; whence I in- 
ferred that those also had undergone no change-in their mag- 
netism since the observations on the Euphrates. The deter- 
minations at Port William and Bussora inserted in the general 
table of this report are derived from these four needles. Their 
_ times of vibration have been reduced to a standard temperature, 
the coefficient inthe formula having been ascertained for each 
needle by experiments made since they have been placed in my 
hands. ‘The full details will be communicated in Colonel Ches- 
_hey’s official publication. 
Freycinet, 181'7-1821.—I am most happy in being able to 
-add to this collection the valuable observations of Capt. de 
Freycinet in the voyage of circumnavigation, performed in the 
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