SECT. VI. mean Distance from the Place; and if the Place be North, take two Days, one between the Tenth of December, and Tenth of March, the other between the Tenth of September, and Tenth of December; the former will be the beginning of Spring, the latter of Autumn: but if the Place be in South Latitude, take the Day between the Tenth of June, and the Tenth of September, for the beginning of Spring; but for Autumn, take that between the Tenth of March, Tenth of June; and Winter will begin the Tenth of June, or December, as the Place is South or North.

and

3. IF the Place have lefs than eight Degrees of Latitude, it will have two Summers, two Springs and Autumn, and Winter, except we reckon the Spring between two Summers to be a Part of a long Summer, and then we do as in the former Cafe; but if we reckon there two Summers, and two Springs, according to our Definitions; find, as before, the beginning of Summer and Winter, and take out of the Table four Days at a mean Diftance, and take two of them as before for the beginning of Spring, viz. that which is next to the first of Summer; and for the fecond Summer's beginning, take the Day that is as far from the twenty firft of June, as the firft Summer's beginning.

PROPOSITION V.

In the Temperate and Frigid Zone the four Seafons are almost of the fame Length; but in the Torrid Zone they are unequal; yea one and the fame will be different in different Places there.

THE

THE former Part of the Propofition is plain, because the Sun goes thro' three Signs in each Seafon, and fo the Times will be nearly equal, excepting a few Days, viz. five that the Summer, and four that the Spring, in northerly Places exceeds the Autumn, and Winter and in Places foutherly the Autumn, and Winter exceeds the Summer and Spring as much, because of the Sun's Eccentricity; as we faid before.

2. IN Places under the Equator there are two Summers (and likewife the other Seafons) and both fhort and the two Springs alfo, each having only thirty Days, and both Summers and both Springs have fixty four Days, i. e. two Months, and two or four, Days: but the Autumn and Winter have fifty five Days, and the two Autumn one hundred and ten, and the two Winters as many, i. e. near four Months.

3. THE nearer the Places in the Torrid Zone are to the Equator, they have the longer Summer, and the lefs Winter; and an Autumn and Spring more or lefs ordinary. In Places of lefs than ten Degrees Latitude, the Summer is no lefs than fix Months; and how long each Season is, may be known by the preceding Propofition.

SO far of the celeftial Seafons; but 'tis not from thefe only that Light, Heat, Cold, &c. do flow; there are other Causes, which we fhall now confider.

PROPOSITION VI.

The Sun goes near the Zenith of Places in the Torrid Zone at Mid-day; but at Mid-night goes far from it under the Horizon, and the Places are there almost in the middle of the Earth's Shadow, and the Sun's Rays neither enlighten nor warm their Air.

In the Frigid Zone, as the Sun is a great way from their Zenith even at Mid-day, fo at Night it goes but a little way under the Horizon, and fends feveral Rays by Reflexion into the Air there. In the Temperate Zone the Sun is at Mid-day at an ordinary Distance from the Zenith, and at Night is a good Way under the Horizon in Winter; but fends fome Rays by Reflexion into the Air in the

Summer-time.

TO fhow this by the Globe: elevate the Pole for the Latitude of a Place in the Torrid Zone, or rather put the Poles in the Horizon; and confider the Parallels which the Sun defcribes in revolving, how far they are above, and under the Horizon, and the first Part will be plain.

THEN elevate the Pole for the Latitude of a Place in the Frigid Zone, and you will fee the Parallels are but a little way under the Horizon; which shows the second Part.

AND again elevate for the Latitude of a Place in the Temperate Zone, and you will fee the Truth. of the Third Part.

PROPOSITION VII.

To find the Continuance of Twilight in a given Place, at a given Time.

IT'S Continuance is from the first appearance of Light to the Sun's rifing, and from Sun-fetting to it's Disappearance; which Aftronomers have found by Obfervation to be at eighteen Degrees under the Horizon.

ELEVATE the Pole, to the Latitude of the Place, and find the Sun's Place that Day in the Ecliptic which being marked, and the Mark brought to the Horizon, and the Index of the Hour Circle to twelve, turn the Globe 'till you find, by a Quadrant of Altitude, or a Pair of Compaffes,

Compaffes, that the Sun is eighteen Degrees under the Horizon; and you will fee how many Hours the Index hath paffed: and fo long is the Light in difappearing in the Evening, and in appearing in the Morning; as may be tried in the Eaft, fuppofing the Air to be clear, It will be convenient to give an Example in each Zone.

PROPOSITION VIII.

In Places in the Torrid Zone the Twilight is leaft, and in the Frigid Zone greatest, and in Places in the Temperate Zone, in a Mean between the

two.

FOR under the Equator, and in Places near it, the Twilight, according to the former Hypothefis, is about one Hour; but by Experience 'tis found to be but half an Hour, or a little more; because the Air, being fo grofs there, is not fo high as is requifite to make Twilight at the Depreffion of eighteen Degrees; and besides, the Suppofition of eighteen Degrees requires very fmall Light, fuch as in the beginning of Twilight which by the Vulgar is not counted Twilight.

IN the Frigid Zone the Twilight lasts for several Days, while the Sun is under their Horizon.

IN the Temperate Zone the Twilight lafts three, four, five, or fix Hours, and all Night in fome Places in Summer-time, according as the Places are more or least near the Frigid Zone. These things may be all proved by the Method in the preceding Propofition.

PROPOSITION IX.

A Place being given in the Temperate or Frigid Zone, and another Place in the Torrid Zone, and likewife

E 3

SECT. VI. likewife the Day of the Year, to find the Hour in the Torrid Zone in which the Sun fhall have the fame Altitude (and fo affect the Horizon with Rays of equal Force) as it hath in the Temperate Zone at Mid-day.

ELEVATE the Globe for the Latitude of the Place in the Temperate or Frigid Zone, and bring the Sun's Place to the Meridian, and obferve it's Altitude, and that is the Altitude of the Rays which warm and enlighten that Place.

THEN elevate the Pole for the Latitude of the Place in the Torrid Zone, and applying the Quadrant to the Zenith, mark on it the Altitude before found, and bring the Sun's Place to the Meridian, and the Index of the Hour Circle to twelve, and move the Globe and Quadrant 'till the Sun's Place agree with the marked Degree of Altitude, or the Quadrant, and the Index will fhow the Hour fought; and therefore the Rays falling in both Places with the fame Obliquity, there is the fame Degree of Light and Heat in both Places, except other Caufes hinder it. viz. 1. That the Sun had before introduced a Temper into the Air of the Torrid Zone, which it had not into the the other Zones. 2. The Sun rifing up more directly in the Torrid Zone, the Rays are all fent almoft the fame way; which will caufe greater Heat than if it had afcended obliquely, and fent the Rays a great many Ways, which difperfes them; whereas Heat requires they fhould be gathered together.

FOR Example; Let us find out in the equinoEtial Day, and Hour when the Sun is as high above the Equator as at Amftardam at twelve o' Clock that Day.

PROPO