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Antiqua
Antiqua (mit lang-s); Auszeichnung: Kursivierung, Kapitälchen; Schmuck: Initialen; Tabellensatz; Besonderes: astronomische Sonderzeichen.
A FEW weeks after my arrival in
tranſmitted to
obſervations, becauſe I hoped that ſome of them might be
intereſting to the Board of Longitude: as I have, however,
learned that the brig by which I ſent my letters was wrecked
near
theſe regions, I think it neceſſary to tranſmit to you a copy
of them.
After a paſſage of about ſix weeks, in the frigate
I arrived at the coaſt of
to the
withſtand the ſtrong deſire I had of ſeeing the wonders of the
Oronoko, and the lofty
high land of
As I have now returned from a very intereſting journey to
the interior of
meri, and
never before viſited by any naturaliſt, during which I carried
with me, on three mules, my aſtronomical inſtruments, viz.
a quadrant by
ters, by
that I have done a great deal for aſtronomy; but you know
that this ſcience is too remote from my principal objects—
philoſophy in general, geology, eudiometry, and the phyſi-
it is impoſſible to labour ſo inceſſantly as under 49°. I choſe
rather to make a few obſervations with accuracy, than a great
many imperfect ones; and to inſert them with great minute-
neſs in my journals, that in caſe I ſhould die in the courſe
of my travels, no doubt might remain in regard to their
exactneſs.
In the two papers which I tranſmitted to
will find my obſervations made in
inclinatorium. I found by it, that local circumſtances have
a greater influence on the inclination of the magnetic needle
than on its declination; and that no connection ſeems to
exiſt between the ſituation of the place of obſervation and the
inclination. This I find confirmed in the
interior of
made by
clination, however, is affected by local cauſes, but much leſs:
at ſea they are much more regular, and the variations are
much more uniform.
I have here given you my obſervations of the inclination
only, which are true to 15′. During calms I obtained them
at ſea with more accuracy, and the periods of the vibrations
of the needle could be determined very exactly. If the ſame
number is counted in the ſame time during five or ſix repeated
trials, and if this is ſtill the caſe when the inſtrument is
moved from its place, the reſults, in my opinion, may be
confidered as correct. Though calms are not uncommon
between the tropics, during the courſe of forty days I was
able to make only ten very accurate obſervations.
In the year 1776, according to
the needle in the undermentioned latitudes and longitudes
was as follows:
Since
with obſerving the declination, I know no place in the earth
where the declination has been determined with certainty to
10″, and not ten where it has been determined to 1′. What
uncertainty ſtill prevails reſpecting the real declination of the
needle at
will ſerve hereafter to determine whether the inclination
ſpeedily changes. The longitude and latitude of the places
of obſervation were always accurately determined at the time
by means of a
conds; and a
them that the inclination decreaſes very rapidly from the
latitude of 37°, and that it increaſes leſs towards the eaſt
than to the weſt from the latitude of 37° to 48°.
It appears to me, that in the higher chain of the calca-
reous mountains of this province, not far from the
ſmall elevations above the level of the ſea derange the in-
clination much more ſtrongly than the higher mountains in
the
give obſervations made at four places which lie pretty nearly
in an arch from north to ſouth (comprehending 24′.)
up for the men of ſcience who accompanied
the intenſity of the magnetic power is the ſame all over the
earth; as he aſcribes the ſmall variation which he found in
it at
compaſs. He requeſted me to verify this circumſtance. You
ten minutes, though it does not decreaſe with the inclina-
tion. This decreaſe cannot certainly be aſcribed to any
change in the goodneſs of the needle, or to other accidental
cauſes: for the ſame needle made in the ſame time at
245 vibrations; at
lentia, 235; and, after a journey of ſeveral months, gave at
the ſame places exactly the ſame number of vibrations as
before my departure. Theſe are always the ſame, in the
open fields, in the houſe, or in a cavern, ſo that the mag-
netic power in any place is always the ſame, and remains a
long time without change; and ſeems to be a general power,
like that of gravity.
I had the mortification of not being able at ſea to make
any good obſervations of the declination. Notwithſtanding
all the trouble I took, I could not find an azimuth compaſs
on which I could depend within 40′. This is the true reaſon
why I have made no mention to you of the declination at
ſea. The point, however, where the inclination vaniſhes,
certainly lies further to the weſt than marked in
chart, in the
obſervation, made in the year 1775 aboard an
from
north, long. 66° 40′ weſt. I obſerved, with great care, the
declination at two places on the coaſt of
compaſs by
thread, according to the method of
At noon, October 1799, it was at
leagues further eaſt, 4° 13′ 45″ eaſt: at
place of the Capuchin miſſion among the Chaimas and
Caribs, 3° 15′ eaſt.
During the earthquake at
vember 1799, the inclination of the magnetic needle was
altered, but not the declination. The former, before the
ſhock, was 44°·20 of the new diviſion; after the ſhock it
remained at 43°·35. The number of the vibrations of the
dipping needle, however, was the ſame as before, viz. 229 in
ten minutes. This, united to other obſervations, ſeems in my
opinion to prove, that during the earthquake this ſmall part
of the ball of the earth was changed, and not the needle;
for, in diſtricts where no ſigns of an earthquake ever appeared
in the primitive chain of accumulated maſſes of granite, the
inclination was as great after as before.
On account of the intereſt which you take in every thing
be unacceptable.
I have carefully proved what Dr.
Society
vering ſhallows at ſea; and am able to confirm, in the fulleſt
manner, what they have ſaid. I was aſtoniſhed to ſee how
the water became evidently colder as its depth decreaſed, and
how the neighbourhood of ſhallows, and of the coaſts, could
thereby be announced. The worſt ſpirit of wine thermo-
meter, if only ſenſible, will therefore, in the hands of the
moſt ignorant mariner, be a very uſeful inſtrument in the
night-time, and during ſtorms, or when it is difficult or
impoſſible to heave the lead. This obſervation I cannot too
ſtrongly recommend to the attention of the Board of Longi-
tude. Our whole crew were aſtoniſhed to ſee how ſpeedily
the thermometer fell, when we approached the large bank
which extends from
garita. Theſe obſervations may be made with more eaſe, as
the water of the ſea, in an extent of 12000 ſquare miles, has
always the ſame temperature day and night; ſo that the moſt
ſenſible thermometer, during from four to ſix days ſail, does
not riſe or fall above 0·3°. In the neighbourhood of ſhal-
lows it was from 2 to 3 degrees, and more, colder. This
obſervation of
period be of great uſe to navigation; not that ſeamen ſhould
throw aſide the lead entirely, and truſt to the thermometer,
for this would be folly; but becauſe the obſervations may be
ſo eaſily repeated, and becauſe the thermometer will an-
nounce the danger much ſooner than the lead, as the colder
water above the ſhallows leſſens the temperature in the water
in the neighbourhood. I can aſſert that this new mean is
not more uncertain than the log, and the helps already em-
ployed in navigation. If the thermometer does not fall, na-
vigators ought not to
from ſhallows; but if it falls, they muſt be on their guard.
This warning is certainly more valuable than our ſea charts,
where the ſhallows are in general laid down in a very in-
correct manner; and to immerſe a thermometer in a bucket
filled with ſea water is certainly much eaſier. I have alſo
meaſured ſeveral timeſ the ſpecific gravity and temperature of
the ſea water, at the ſurface and at certain depths, by means
of
caſes furniſhed with a valve. As my inſtruments were com-
pared with the beſt Pariſian ones, and as I could be more
chart in which I intend to make known the reſult of theſe
experiments will be intereſting. In the latitude of 17° and
18° north, there is a zone in the ſea between
Weſt Indies, where, without an extraordinary current pre-
vailing, the water is denſer than under a leſs latitude. The
following are ſome of my reſults reſpecting the temperature
of the ſea water:
This letter was written at
proper opportunity I was obliged to bring it with me to this
large capital of the province of
in a fertile valley abounding with cacao, cotton, and coffee,
2400 feet above the level of the ſea, and in a climate per-
fectly ſimilar to that of
night-time falls to 11°, and in the day never riſes above 17°
or 18°.
The cloudy weather, which here daily follows the ſun’s
paſſage over the meridian, makes the obſervation of corre-
ſponding altitudes very difficult and uncertain, as the after-
noon obſervation is often loſt. The cloudy weather after the
earthquake of
ſerving the immerſions of the ſecond ſatellite of
the 2d and 9th of November. I ſhall here give you the prin-
of
I ſhall here alſo mention, that neither wind, ſtorms, nor
the earthquake, have had the leaſt influence on the regular
daily variation in the ſtate of the barometer; and that, ac-
cording to C.
rinam to two lines.
Theſe obſervations are the more intereſting, as all the charts
of this part of the world are very incorrect; and the agree-
ment of my longitude of
ſervations of
time, is a proof of the excellence of my chronometers.
The ſerenity of the nights between the tropics gave me an
opportunity of comparing with each other the ſtrength of the
light of the auſtral ſtars; which in ſome of them, ſuch as
the Crane, Altar, Toucan, and the Foot of the Centaur, ſeems
to have changed ſince the time of
the method propoſed by Dr.
the ſame kind as thoſe uſed for the ſatellites. If the light of
the light of the following ſtars, according to my obſervations,
are as below expreſſed.