19. _Oblique Ascension_, or _Descension_, is an arch of the equinoctial intercepted between the beginning of ♈, and that _Point_ of the _Equator_ which rises or sets with any point in the Heavens in an oblique sphere.
20. _Ascensional Difference_, is the difference betwixt the right and oblique ascension or descension, and shews how long the Sun rises or sets before or after the hour of six.
The parts that time is distinguished into, are _Days_, _Hours_, _Weeks_, _Months_, and _Years_.
[Sidenote: _Natural_ and _Artificial Day_.]
A _Natural Day_ is the space of time elapsed while the Sun goes from any meridian or horary circle, ’till he arrives to the same again; or, it is the time contained from noon, or any particular hour, to the next noon, or the same hour again: An _Artificial Day_ is the time betwixt the Sun’s rising and setting; to which is opposed the _Night_, that is, the time the Sun is hid under the horizon.
[Sidenote: _Vernal_ and _Autumnal Equinox_.]
[Sidenote: _Summer_ and _Winter Solstices_.]
The _Natural Day_ is divided into 24 _Hours_, each hour into 60 _Minutes_, each minute into 60 _Seconds, &c._ The _Artificial Days_ are always unequal to all the inhabitants that are not under the equator, except when the Sun is in the equinoctial points ♈ and ♋, which happens (according to our way of reckoning) about the 21st of _March_, and the 23d of _September_; at those times the Sun rises at six and sets at six to all the inhabitants of the Earth. These days are called the _Equinoxes_, or _Equinoctial Days_; the first of which, or when the Sun is in the first point of _Aries_, is called the _Vernal Equinox_, and the latter is called the _Autumnal Equinox_. In all places where the Sun descends below the horizon, excepting under the equator, the days continually lengthen or shorten, and that faster or slower, according as the Sun is nearer to, or further from the equinoctial, until he arrives to either of the _Solstitial Points_ ♋ or ♑. At those times the Sun seems to stand still for a few days, and then begins to return with a slow motion towards the equinoctial, still hastening his pace as he comes nearer to it: The Sun enters the tropics of ♋ and ♑, about the 21st of _June_, and the 22d of _December_, which days are sometimes called the _Solstices_; the first of which we call the _Summer Solstice_, and the latter the _Winter Solstice_.