75 
magnetical observations at Port Bowen , &c. 
other end of the silk, in order to adjust it so that it might 
barely touch the centre or point of support. 
No. 3 needle, which was that of a common ship's azimuth 
compass, and weighed 146 grains, was suspended like the 
other two, but simply contained within an air-tight box 
having glass ends. A sight of card paper being fixed 
towards each extremity of the needle, the amount of varia- 
tion was obtained, by observing the coincidence of the sights 
through a small telescope traversing upon an arc of ten fee 
radius, and consequently placed at that distance from the 
needle. A vernier attached to the telescope, and moving with 
it, gave the reading to the nearest minute. This needle was 
afterwards used exclusively for obtaining the changes in the 
magnetic intensity, for which it was found remarkably well 
adapted ; the instant of the coincidence of the two sights being 
easily observable through the telescope to two-tenths of a 
second, by means of a chronometer held to the ear. During 
the absence of day light, these observations were made by can- 
dlelight, transmitted through a sheet of oiled paper, fixed 
against the glass end of the box, farthest from the observer. 
The observations were made at the commencement by 
Lieutenant Foster and Captain Parry, but were subse- 
quently carried on in regular watches, and the needles visited 
every hour during four successive months, by Lieutenants 
Sherer and Ross, and Messieurs Crozier, Richards and 
Head. When any extraordinary change, however, appeared 
to be going on, the needles were more closely watched ; 
and every phenomenon, such as the aurora borealis, meteors, 
clouds, the kind and degree of light, the moon's position, and 
the temperature within and without, were at all times care- 
