“ The local attraction of the Beagle will of course have
been ascertained before she leaves England ; hut when favourable
opportunities occur, it will he satisfactory to swing her
again in different latitudes, and under large differences of
variation.
“ No day should pass at sea without a series of azimuths,
and no port should be quitted without having ascertained not
only the magnetic angle, hut the dip, intensity, and diurnal
variation. I f these observations should have been well made
in the same places before, we shall at once obtain the annual
change ; and by multiplying them in new places, we shall have
the means of inferring the magnetic curves.
“ The Commander has been so accustomed to the management
of chronometers, that there is no doubt, with proper precautions
and with proper formula; for determining their rates,
that he will succeed in obtaining good results in reasonably
short intervals of time and in gradual changes of temperature ;
but after long periods, and sudden changes of heat and cold,
it will be absolutely necessary to check them by astronomical
means.
“ Eclipses, occultations, lunar distances, and moon-culminating
stars, will furnish those means in abundance : of all
tliese, the last can he obtained with the greatest regularity and
certainty ; they have become part of the current business at
the establishments of the Cape of Good Hope, Paramatta, and
St. Helena, in the southern hemisphere ; probably at Madras,
and in many of the European observatories, and it will therefore
be scarcely possible that there should not be corresponding
observations for all such as he may have made.
“ The eclipses of Jupiter’s third and fourth satellites should
also he sedulously observed whenever both immersion and
emersion can be seen, as the different powers of the telescopes
employed by the observers do not in that case affect the
results.
“ There are also some remarkable phenomena, which will he
announced in the Nautical Almanacks, and which will occur
during the Beagle’s voyage. Some of these will be highly
interesting to astronomers, and if it w'ould not much derange
her operations, she should be taken to some convenient anchorage
for the purpose of landing the instruments.
“ I f a comet should be discovered while the Beagle is in
port, its position should be determined every night by observing
its transit over the meridian, always accompanied by the
transits of the nearest known star's, and by circiim-nieridional
altitudes, or by measuring its angular distance from three well-
situated stai's by a sextant. This latter process can be
effected even at sea, and the mean of several observations may
give very near approximations to its real position.
“ Meteorological Registers may be of use in a vai'iety of
ways ; but then they must be steadily and accurately kept.
The barometer should be read off to the third place of decimals,
and recorded at regular periods of the day ; nine o’clock and
four o’clock may be recommended as the best, as being the
usual hours of its maximum and minimum. The temperature
should be marked at the same time, and the extremes of the
self-registering thermometer should be daily recorded; care
being taken that no reflected heat should act on any of these
instruments. The temperature of the sea at tlie surface ouglit
to he frequently observed and compared with that of the air.
An ofiicer cruizing on the east coast of South America, between
the parallels of 20“ and 35“, was enabled by these means
to predict with singular precision the dh'ection and strength of
the current.
“ In this register the state of the wind and weather will, of
coui'se, be inserted; but some intelhgible scale should be
assumed, to indicate the force of the former, instead of the
ambiguous tem s ‘ fresh,’ ‘ moderate,’ &c., in using which no
two people agree; and some concise method should also be
employed for expressing the state of the weather. The suggestions
contained in the annexed printed paper are recommended
for the above purposes, and if adopted, a copy should be pasted
on the first page of every volume of the iog-book ; and the
officer of the watch should be directed to use the same terms in
the columns of the log-board.
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