378 O B S 
the atmofphere. The clocks are attached to pillars of the 
greatest fteadi'nefs alfo : they were made by Arnold, who 
exerted his belt Skill, and are finished in a mafterly man¬ 
ner : the pallets are of ruby ; and all the laft holes of the 
movement jewelled ; the fufpenfion-fprings are of gold, 
with Arnold’s own five-barred pendulum, and cheeks ca¬ 
pable of experimental adjuftment, fo as to make all vi¬ 
brations ifochronal, whatever may be the excurfion of the 
pendulum. 
At Armagh, the metropolitan city of Ireland, and an¬ 
ciently the feat of a large univerfity, there has been an 
obfervatory ereCted and endowed in 1793, by Richard lord 
Rokeby, then primate of all Ireland. It is ereCted on 
the fummit of a gently-riling hill, about 90 feet above the 
general level of the town, and furrounded by feveral un¬ 
dulating hills, all nearly of the fame altitude. This build¬ 
ing is founded on a bale of limeftone, and all the walls 
are of large hewn ftone, and of the molt firm and fub- 
fcantial w'orkmanlliip. The tower, which joins the dwell- 
ir.g-houfe, contains a very fine equatorial by Troughton, 
fixed upon a large pillar, wdiich is railed fo high, that the 
instrument in the dome can overlook all the buildings. 
To the ealt of the houfe is a range of buildings, for the 
tranlit-room, and other altronomical purpofes. The prin¬ 
cipal inltruments, beiides the equatorial and tranfit, are 
a ten-feet fextant by Troughton ; a ten-feet reflecting te- 
1 -efcope by Dr. Herfchel ; a five-feet triple objedt-glafs 
achromatic telelcope by Dollond ; and alfo a fine night- 
glafs, upon an equatorial Itand. The clocks are by Earn- 
fhaw of London, and Crofsthwaite of Dublin. In this 
eltablilhment a liberal income is allowed to the principal 
altronomer, and a good falary to his afliltant. It has been 
fuperintended from the beginning by the Rev. James 
A-rcnibald Hamilton, D.D. dean of St. Coleman’s, Cloyne, 
v. ho has contributed feveral learned papers to the Tranf- 
aCtions of the Royal Irilh Academy, chiefly on aftronomi- 
cal fubjeCts. His obfervations, particularly on the fixed 
liars, are confidered very accurate; and fome of his de¬ 
clinations have been tranfcribed into the Philofophical 
TranlaCtions of the Royal Society of London in 1806. 
The registered obfervations here are thofe made with the 
tranfit-inftrument and equatorial ; and alfo an account of 
the temperature and weight of the atmofphere. Of thefe, 
a feries of about eighteen years is preferved. Monthly Mag. 
Sept. 1813. 
Direttions for Building and Furnijhing Olfervatories .— 
Tn building an obfervatory, attention Should be paid to 
Situation, foil, and foundation, as well as to ftrufture; 
and in furnilhing one, regard mull be had both to the 
proper choice, and convenient difpofition, of inllruments. 
The Situation fhould be fufficiently elevated to command 
a view of the horizon, efpecially to the north and fouth ; 
but very high places are not eligible, as they moftly at¬ 
tract clouds, and are in other relpeCts too much expofed 
to the feverities of weather. In chooSing a fituation, it will 
be requisite alfo, to make preparation for a meridian-mark, 
and for this purpofe it would be convenient, if the obfer¬ 
vatory could be placed in the meridian-line of fome build¬ 
ing, or other permanent objeCt, upon which the mark may 
be made, and this is done as foon as the tranfit-inftru- 
ment is fet correCtly in the meridian, by which it may be 
afterwards regulated. If two meridian-marks can be fet 
up, one north, and the other South, it will be definable ; 
and they Should not be lefs than 500 yards diftant from 
the obfervatory ; the farther the better, provided they are 
vifible. The obferver flrnuld have free accefs to them, as 
it may benecefiary fometimes to illuminate them by night. 
Thefe marks ought to be nearly on the fame level, and 
not fubjeCt to be obfcured by grofs exhalations, as Inch 
are luppofed to create horizontal refractions, and to make 
the marks appear out of the meridian. 
The foil Should be naturally dry, which is generally the 
cafe when it is of a gravelly or llony kind 5 but clay-foils, 
that do not foon abforb the rain, caufe exhalations and 
damps, which not only injure the instruments, and ob- 
O B S 
fcure the atmofphere, but greatly increafe the irregula¬ 
rities of refraCtion. The foundation fhould be of the 
molt folid kind ; and therefore a rock of fome extent, or 
a hard gravel, Ihould be chofen ; and, where Such cannot 
be had, all adventitious firmnefs Ihould be obtained, ei¬ 
ther by conftruCting deep arches, or by piles driven with 
an engine ; for fuch is the perfection of modern instru¬ 
ments, that they immediately betray any defeCt in the 
building, whether arifing from the foundation or the fu- 
perftrufture. The.building Should Therefore be of Solid 
and Substantial mafonry, particularly the tranfit-room, 
which is the mod effential apartment of an obfervatory. 
This room Should, for the fake of firmnefs, be on the 
ground ; and the pillars which fupport the instruments 
and clocks, Should be detached from the floor. It fhould 
of courfe poflefs a good view both north and fouth; and 
the opening or meridian aperture, for obferving through, 
fhould command an uninterrupted view from the zenith 
to the horizon, in both directions; and the Shutters, or 
covers of the apertures, fhould be opened and Shut with 
eafe by pulleys, or other ready methods. The proper 
w'idth of the meridian apertures has been a fubjeCt of 
Some doubt; but it is generally agreed that they Should 
be wide enough for pointing the instrument conveniently 
to the heavens, and for admitting a ready fupply of freSh 
air into the obfervatory, fo as to render the internal tem¬ 
perature equal to the exterr,al ; and, if the Shutters be di¬ 
vided into Small openings, Such may be occasionally ufeful, 
to prevent a very hot fun from affeCting the adjuftment 
of the instrument. With refpeCttothe other apartments, 
their number mull depend on the number of instruments 
to be ufed, whether at the fame time or in fuccefiion. In 
molt large observatories, there is a dome raifed, for the 
equatorial or the circular instruments. 
As to the choice of infiruments, and their convenient 
difpofrtion, regard mult be had to the plan of building; 
and the number muft alio depend on the fame, as well as 
on the number of obfervations to be made. An obfer¬ 
vatory, however, cannot be confidered as well furnished 
without the following apparatus : a tranfit-inftrument, or 
mural tranfit-circle, with good clocks to Show both Solar 
and Sidereal time ; and chronometers are often ufeful. 
Mural quadrants or fextants may be likewife mentioned ; 
but entire circles are greatly preferable, as they admit of 
various lelf-correfting adjustments, particularly when 
fitted-up with revolving microfcopes. A portable reflect¬ 
ing circle fhould alfo form part of the apparatus, in order 
to mealure angular distances in all directions, horizontal, 
vertical, and oblique. If there be a circular instrument 
that will mealure both altitudes and azimuths, or an equa¬ 
torial instrument, then a movable dome will be neceffary. 
A zenith-feCtoris likewife of importance-; and, of courfe, 
good telefcopes are elfential, efpecially an achromatic with" 
an equatorial movement and a micrometer eye-piece; alfo 
a powerful refleCtor, for obferving the phafes of the Sun, 
moon, and planets, as well as the fateilites, nebulse, &c. 
See the articles Astronomy,-Greenwich, Maskelyne, 
Optics, &c. 
OBSER'VATORY I'SLAND, a finall island in the 
Straits of Magellan, at the entrance of Bougainville’s Bay. 
OBSER'VATORY I'SLAND, or Padevou'a, a Small 
island in the South Pacific Ocean, near the north-eaft coalt 
of New Caledonia. Lat. 20. 18. S. Ion. 165. 41. E. 
OBSER'VATORY POI'NT, a cape on the north coaft 
of the island of Tongataboo. Lat. 21.8. S. Ion. 184.. 55. E. 
OBSER'VATORY IN'LET, an inlet on the weft coaft 
of North America, where Capf. Vancouver made his ob¬ 
servations. It extends about thirty-two miles. Lat. 54. 
58. N. Ion. of the entrance 230. 6. E. 
To OBSER'VE, v. a. [obferver , Fr. ohfervo, Lat.] To 
watch; to regard attentively.—Remember, that as thine 
eye obferves others, So art thou obferved by angels and by 
men. Bp. Taylor. —To Sind by attention ; to note.—It is 
obferved, that many men who have feemed to repent when 
they have thought death approaching, have yet, after it 
hath 
