Page:Cyclopaedia, Chambers - Volume 2.djvu/454

 POL

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CMir-Poiso*!, SeeCouNTER-F«/o».'

To P o 1 s o n a Piece, among Gunners, is the fame as to clog and nail it up.

POISONING, in Law, the Crime of adminiftring Poifon to a Perfon.

This, by a Law of Henry VIII. was made High-Treafon; but that Law was afterwards repealed; and the Punifliment made for it was to be put alive into a Cauldron of Water, and

toil'd to Death. At prefent it is only Felony without

Benefit of Clergy. See Punishment. •

POLAR, Something belonging to the Poles of the World. See Pole.

In this Senfe we fay, Volar Virtue, Volar Tendency, &e. See Polarity.

Polar Circles., are two Circles parallel to the Equa- tor, at the Diftance of 23 Deg. from each Pole; ferving to mark the beginning of the Frigid Zone. See Circle and 'Zone.

The Volar Circles are particularly denominated from their refpeftive neighbouring Poles, the Artlic and Antartlic. See Arctic and Antarctic.

Polar Dials are thofe whofe Planes are parallel to Tome great Circle palling through the Poles, or to Tome one of the Hour-Circles; fo that the Pole is neither elevated above, nor depreffed below the Plane.

Such Dial therefore can have no Center, and confequent- ly its Style, Subftyle, and Hour-Lines are parallel. See Plane.

This therefore will be an Horizontal Dial to thofe who live under the Equator or Line.

To conflruli a Polar Dial. See Dial.

Polar Projection is a Reprefentation of the Earth or Heavens, projected on the Plane of one of the Polar Cir- cles. See Projection.

P O L A R I T Y, the Quality of a Thing confidered as ha- ving Poles. See Pole.

By heating an Iron Bar, and letting it cool in a vertical

Pofture, it acquires a Polarity. The lower End becomes

the North End; the upper the South. See Iron.

Iron Bars acquire a Volarity, by being kept a long

time in an erect Pofture, even without Heating Thus

the Bars of Windows, &c, are frequently found to have Poles. Nay a Rod of Iron acquires a Volarity, by the mere holding it ereft; the lower End in that Cafe attract- ing the South End of a magnetic Needle ■, and the upper

the North End. But thefe Poles are mutable, and fhifc

with the Situation of the Rod. See Magnet and Mag- netism.

POLE, Polus, in Aftronomy, the Extremity of the Axis whereon the Sphere revolves. See Axis and Sphere.

Thefe two Points are called, by way of Excellence, the Poles of the World. See World.

The Word is form'd from the Greek WiSt, vertere, to turn.

Wolfius defines the Voles, thofe Points on the Surface of the Sphere through which the Axis palTes: fuch are the

Points P Q, (Tab. Aftronomy, Fig. 52.) ■ whereof, that vi-

fible to us, or rais'd above our Horizon P, is called the Artlic or North Vole; and itsOppofite Q, the Antarctic or South Vole. See Arctic and Antarctic.

Pole in Geography, is the Extremity of the Earth's Axis-, or the Points on the Surface of our Globe, thro' which the Axis pafles. See Earth.

Such are the Points P Q, (Tab. Geography, Fig. 7.) where- of that Elevated above our Horizon P, is called the Arctic or North Vole; and its Oppofite Q, the Antartlic or South Pole. See Globe.

Dr. Halley fhews, that the foliftitial Day, under the Vole, is as hot as under the Equinoctial, when the Sun is in the Zenith; in regard all the 24 Hours of that Day under the Pole, the Sun's Beams are inclined to the Horizon with an Angle of 23i Degrees; whereas, under the Equinoctial, tho' he becomes vertical, yet he fliines no more than 12 Hours, and is abfent 12 Hours. befides, that for 3 Hours 8 Mi- nutes of that 12 Hours he is above the Horizon there, he is not Co much elevated as under the Vole. See Heat.

The Altitude or Elevation of the Vole, is an Arch of the Meridian, intercepted between the Vole and the Horizon. See Altitude.

To find this Elevation is a very popular Problem in Aftro- nomy, Geography, and Navigation-, This and the Latitude of the Place being ever the fame. See Latitude.

To cbferve the Altitude of the Pole.

With a Quadrant, obferve both the greateft and lead Me- ridian Altitude of the Vole-Stu. See Meridian.

Subftract the leaft from the greateft, and divide the Dif- ference by two •, the Quotient is the Star's Diftance from the Vole; which added to the leffer Altitude found, gives the Elevation of the Vole required.

Thus M. Couplet the younger, at Vl'fyppOy m l ^97i at the

End of September, obferv'd the greateft Meridian Alritiide 40 5' 40", The fmalleft, 36 28' o". The Difference whereof is 4 37*40"; one half whereof, z° 18' 50", added to the lefs, gives 38 46' 50", The Altitude of the Pole of Vlyffppo. See Altitude.

The Altitude of the Vole; together with the Meridian Line, being the Bads of all Aftronomical Obfervations; to determine it with the greater Accuracy, the Meridian Alti- tudes mult be corrected from the Doctrine of Refractions, hereafter delivered. See Refraction, Meridian, &c.

By Means hereof, M. Couplet fubftracting l' 2i" in the propofed Example, leaves the corrected Altitude 38°45' 25''.

Hence 1. The Altitude of the Pole being fubftrafted from 90, leaves the Altitude of the Equator. See Equator.

2. If the greateft Meridian Altitude of this Star exceed the Altitude of the Equator, the latter fubftracted from the former, leaves the Declination of the Star Northward; If the Altitude of the Star be lefs than that of the Equator; the former fubftracted from the latter leaves the Star's De- clination Southward. See Declination.

Dr. Hook, and Tome others, imagined, the Height of the Pole, and the Pofition of the Circles of the HeavenSj in refpect of thofe on the Earth, to be changed from what they anciently were : But M. Cajfini thinks there is no Ground for fuch Surmife; but that all the Difference we now find in the Latitudes of Places, &c, in refpect of the ancient Accounts, arifes from the inaccuracies of the an- cient Obfervations.

Indeed 'tis no wonder they fhould err in their Obferva- tions, confidering what Inltruments they ufed : He adds; 'tis probable there may be fome Variation in the Height of the Vole; but thinks this never exceeds two Minutes; and that even this will vanifh, after it is arrived to its higheft Difference. See Equator, &c.

Pole, in Sphericks, is a Point equally diftant from every Part of the Circumference of a greater Circle of the Sphere; as the Center is in a plain Figure. See Center.

Or, Vole is a Point oo° diftant from the Plane of a Circle, and in a Line palling perpendicularly thro' the Cen- ter, called the Axis. See Circle.

The Zenith and Nadir are the Poles of the Horizon—^ The Poles of the Equator are the fame, with thofe of the Sphere or Globe. See Zenith, Nadir, &c.

Poles of the Ecliptic are Points in the Solftitial Colure 23 30' diftant from the Poles of the World. See Sphere, Equator, Horizon, &c.

Poles in Magneticks, are two Points in a Loadftone,' correfponding to the Poles of the World; the one pointing to the North, the other to the South. See Magnet.

If the Stone be broke in ever fo many Pieces, each Frag- ment will have its two Poles. If a Magnet be biffeeted

by a Line perpendicular to the Axis; the two Points before join'd will become oppofite Voles, one in each Segment.

To touch a Needle, &c. that Part intended for the North Endistouch'dwith the South We of the Magnet, and that in- tended for the South End with the North Vole. See Needle.

A Piece of Iron acquires a Polarity, by only holding it upright, &c See Polarity. But its Voles are not fix'd;

but fhift, and are inverted as the Iron is A fix'd North

Vole may be made all the Ways a fix'd South Vole is made; but not vice verfa; and whatever Way we get a fix'd South Pole, 'tis always weaker than a fix'd North Vole got the fame Way.

Fire deffroys all fix'd Voles; but ftrengthens the mutable ones. See Fire.

The End of a Rod being heated, and left to cool North- ward, Dr. Gilbert fays, becomes a fix'd North Vole-, if Southward, a fix'd South Pole: yet this does not hold in

all Cafes.. If the End be cool'd held downward or to the

Nadir, it acquires fomewhat more Magnetifm, than if cool'd horizontally towards the North. But the bed Way is to cool it a little inclined to the North. Repeated Ignitions don't avail more than a iingle one.

Dr. Power fays, that if we hold a Rod Northwards, and hammer the North End in that Pofition; it will become a fix'd North Vole; and, contrarily, if you hammer the South

End What is faid of Hammering is to be likewife un-

derftood of Filing, Grinding, Sawing; nay, a gentle rub- bing, provided it be continued long, will produce Poles. See Friction.

The more heavy the Blows are, ceteris paribus, the Mag- netifm is the ftronger. A few hard Blows do as much as

many. Old Drills and Punches are fix'd North Poles, be- caufe almoft conftantly ufed downwards. New Drills are either mutable Poles or weak North Poles. Drilling with fuch a one Southward horizontally, 'tis a Chance if you produce a fix'd South Pole, much lefs if you drill South downwards; but if you drill South upwards, you make a fix'd South Pole.

A weak fix'd Pole may degenerate into a mutable one in

a Day; nay in a few Minutes, by holding it in a Pofition

contrary to its Pole. The Loadftone itfelf will not make a

10 F fix'd