Page:Cyclopaedia, Chambers - Volume 2.djvu/935

 V A R

VARIANCE, in Law, an Alteration or Change of Con- dition in a Perfon, or Thing ; after fome former Concern or Tranfaftion therewith.

Thus, if the Commonalty of a Town make a Compofi- tion with a Lord, and afterwards Bailiffs be granted by the King to the fame Town ; there, if the Lord commence any Suit for breach of the Compofition, he mufi vary from the Word Commonalty, ufed in the Compofition ; and ufe 'Bai- liffs and Commonalty.

TheTetm Variance is alfoufed for an Alteration of fome- thing formerly laid in a Plea. See Plea.

VARIATION, in Geography, Navigation, i§c. a Term apply'd to the Deviation of the Magnetical Needle, or Com- pals, from the true North-Point, towards either Eaft, or Well; call'd alfo the 'Declination. See Declination.

7*/>e Variation or Declination of the Needle, is properly defin'd, the Angle which a Magnetic Needle, fufpended at liberty, makes with the Meridian-Line on a horizontal Plane. See Neeele.

In the Sea Language, the Variation is ufually called North-Eaft-ing, or North-Wefting. See Compass, f$c.

All Magnetic Bodies, we find, range themfelves, in fome fort, to the Meridian ; but 'tis rare they fall in precifely with it : In one Place, they decline from the North to the Eaft, and from the South to the Weft; and in another Place, on the contrary, from the North to the Weft, and from the South to the Eaft ; and that, too, differently, at different Times. See Magnet, and Magnetism.

Various are the Hypothefes fram'd to account for this ex- traordinary Phenomenon : We /hall only mention fome of the later and more probable. The firft is that of Gilbert, which is follow'd by Cabeus, &c.

Their Notion was, that 'tis the Earth, or Land, that draws the Needle out of its Meridional Direction ; and hence they argued, that the Needle vary'd more, or lefs, as it was more or lefs diftant from any great Continent : con- fequently, that if it were placed in the middle of an Ocean, equally diftant from equal Tra&s of Land, on each fide, Eaftward and Weftward, it would not decline either to the one or the other; but point juftly North and South.

Thus, in the Azores Iflands, which are equally diftant from Africa on the Eaft, and America on the Weft, there is, in effect, found no Variation : but, as from the Azores you fail towards Africa, the Needle begins to decline from the North to the Eaft ; and that ftill more and more, till you reach the Shore.

If you ftill proceed Eaftward, the Declination gradually diminifhes again ; by reafon of the Land left behind on the Weft, which continues to draw the Needle.

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V A R

The fame holds till you arrive at a Place w^here there are equal Trafts of Land on each fide, and there, again, there is no Variation.'

The Obfervations of our Mariners in their Eafi-India Voyages, feem to confirm this Syftem : As they proceed to- wards the Cape of Good Hope, the Variation is ftill Eaftward - at length, arriving at the Cape De las Aguillas, q. d. of the Needles, the Meridian-Line, then, dividing Africa into two equal Parts ; there is no Variation at all : But as they pro- ceed further, and leave rhe African Coafts on the Weft, the Variation becomes Weftward.

But the Misfortune is, the Law does not hold univerfally : In effba, a great Number of Obfervations of the Varia- tion, in various Parts, made and colle&ed by Dr. Halley, overturn the whole Theory.

Others, therefore, have recourfe to the Frame and Corn- pages of the Earth, confider'd as interwove with Rocks and Shelves ; which being generally found to run towards the Poles, the Needle comes to have a general tendency that way ; but which feldom going perfectly in the Direc- tion of the Meridian, the Needle, of confequence, has com- monly a Variation. See Earth.

Others hold various Parts of the Earth to have various degrees of the Magnetic Virtue ; as fome are more inter- mix'd with heterogeneous Matters, which prevent the free Aftion or Effect thereof, than others. See Magnetism.

Others afcribe all to Magnetic Rocks, and Iron Mines, which affording more of the Magnetic Matter than other Parts, draw the Needle more. Sec Iron, i£c.

Laftly, others imagine Earthquakes, or High Tides, to have difturb'd and diilocated feveral considerable Parts of the Earth, and fo chang'd the Magnetic Axis of the Globe, which originally was the lame with rheAxis of the Globe it felf!

But ftill, that great Phenomenon, the Variation of the Variation, i. e. the continual Change of the Declination in one and the fame Place, which the modern Obfervations do abundantly evince, is not accountable for, on any of thefe Foundations ; nor even confiftent with 'em.

Dr. Bailey, therefore, gives us a new Syftem; the Re- fult of a great Number of Obfervations ; and even of a great Number of Voyages made, at the publick Charge, on this very Account : The Light that excellent Author has let into this obfeure Part of Natural Hiftory is very great ; and the Confequences thereof in Navigation, £=?c. very considerable. Add, that he has reduced the divers Variations of divers Places to a precife Rule, or Order, which before appear 'd all precarious, and arbitrary.

His Theory, therefore, will deferve a more ample De- tail.— The Obfervations it is built on, as laid down in the fhtlofophical TranfaSions, are as follow.

Obfervations of the Variations of the Needle, in divers T laces, and at divers Times.

Names of Places.

Longitud

from

London.

Uramburg »^_ — _

Copenhagen

Dantz.Uk —

Montpelier — —

Brefl

Rome ____

rayonne.

Hudson's Bay — —.

Jn Hudfon's Streights (Sound

In Baffin's Bay, at Sir Tho. Smith's

At Sea

At Sea

At Sea —.

Cape St. Augtifline

At Sea off the Mouth of R. Plata

Cape Frio

Eaft Entrance of Magellan Streights

Weft Entrance

Baldivia < ■

2 25 E

OE

53E oE oE

25 W o E

W»

40 w o W o W o W

30 W o W

30 W o W

10 W

Latitude

Year DfOb. ferv.

51 32 N

15'N

54N

41 N

23 N

37 N

2jN

50 N

33N

oN

oN

oN

40 N

(o»

oN

o S

30 S

40 s

30 S

o S

o S

Variation obferv'd.

1580

1^22 I634 1672.

ts8j

1640

I681 1*72 I< 4 9 1679 M74 I58o

i<s8i i«8o

i«S8

1SS8 isi5 1682 168

i«7 HJ70 1 £70 IC-JO 1670

1670 IS70

11 15E

6 oE 4 5E

1 joW

4 30 W 3 oE

o

2 30W

2 J5W-

1 30E

7 oW 1 10 W 1 45 W

5 o W 1 20 Vf

is 15 W

29 30 W

57 oW

7 JO

5 jo W

o 40 E

5 10E

20 30 E

12 10 E 17 oE 14 10 E

~ 10E

Names of Places.

Cape Aguillas

At Sea

At Sea __^_

At Sea

St. Helena

J. Afcenfien

J-ohajma

Monbafa

Zocatra — —

Aden, at the Mouth of the Red Sea

Diego Roi%.

At Sea.

At Sea

nbay ■ 1 ■

C. Comorin __^_«

Ballafore.

Fort St. George

Weft Point of Java

At Sea —

/. St. Paul

At Van Diemem

At New Zealand ■

At Three King Ifle in New Zealand I. Roterdam in the South Sea On the Coaft of New Guinea At the Weft Point of New Guinea

Longitude from London,

Latitude

Year or'Ob- ferv.

Variation obferv'd.

16 30 E

3450S

1622

2 W

W

1675

8 W

1 E

54 5° S

1675

20 W

34 S

1675

10 30 E

32 6 W

24 S

I67S

to 30 -E

630 W

16 s

i«77

40 E

1410 w

7 So S

167S

r E

44 E

12 15 s

1675

1930 W

40 E

4 S

1S7S

l< t>W

56 E

12 3° N

1.574

17 w

47 3° E

Jt oN

1674

l( of

61 E

20 S

1676

20 ;0 W

64 30 E

1676

15 jo W

54 E

27 S

1676

24 W

7230 E

19 ON

1676

12 W

76 E

8 15N

1680

8 48 W

87 E

.1 30 N

t<58o

8 20 DC

180 E

13 15N

t68o

8 10 w

104 E

640 S

1 676

3 10 W

58 E

!9 S

1077

27 30 W

72 E

58 S

1677

.3 30 w

142 E

422, s

1642

170 E

40 50 S

1642

9 E

169 Jo E

343SS

1642

840 E

184 E

20 15 s

1642

620 E

I4S E

430 S

1643

8 45 E

026 s

5 JO E

From thefe Obfervations the learned Author gathers ift, That throughout all Europe, the Variation, at this Time, is Weft; and more in the Eaftern Parrs thereof

than the Weftem, increafing that way. 2d, That on the

Coafts of America, the Variation is Wefterly ■ increafing all the way as you go Northerly along the Coaft ; fo as to be above 20 Degrees at Newfoundland, nearly 30 Degrees in Hudfon's Streights, and not lefs than 57 Degrees in Baf-

fin's Bay .- And that as you fail Eaftward from this Coaft, the Variation dimini/hes. Hence, he argues, fomewhere between Europe and the Notth Part of America, there muft

be an Eafterly Variation, or at leaft no Variation. ■

3d, That on the Coaft of Brazil, there is Eaft Variation, increafing as you go to the Southward, fo as to be 12 Deg. at Cape Frio, and 20 Degrees and half over againft R. 'Plata 5 and thence failing South-wefterly, to the Streights

of