An astrological discourse with mathematical demonstrations proving the powerful and harmonical influence of the planets and fixed stars upon elementary bodies in justification of the validity of astrology : together with an astrological judgment upon the great conjunction of Saturn & Jupiter, 1603 / written by that worthy, learned gentleman, Sir Christopher Heydon, Knight ; and now published by Nicholas Fiske ...

CHAP. V. (Book 5)

The fourth difference caused by the depth or diverse crassitude of the Air by which the Beams pass. (Book 5)

NEither can we be rightly said to * 1.1 have the full fruition of this porti∣on of Heat in Winter, by reason that the crassitude or thickness of the Air is then more object to the Suns oblique Beams then in Summer, and doth there∣by resist and hinder them more now then in Summer. For proof hereof,

[illustration]

Diagram.

let D F H represent the superficies of the Earth: I G N, the convex superfi∣cies of the cloudy or vaporous Region: And suppose the Sun to shine upon F, the place of our habitation, from three several points, Z, A, B. Z being the ver∣tical point over our heads, A the Suns Summer height, B his altitude in Win∣ter (as before was expressed:) So Z F, A F, and B F, shall be the Suns Beams, part whereof, viz. G F, K F, and M F, we see are in a sort obscured, hindered, and resisted by the vaporous Air. But now for as much as (by the 7 of the 3 of Eucli∣de) G F is shorter then K F, & K F then M F, therfore the Sun shal of necessity feel less impediment in the Zenith at Z, then at A, and by consequence at A, then at B. because still the further the Sun is re∣moved from the Zenith, the longer is the passage of the Sun-beams through the opposite air. Now to attain Geo∣metrically to the proportion of the Suns debilitated force, through this impedi∣ment; we are first to agree how deep or thick this cloudy Region of the air that ••efringeth the Sun-beams may be: which our late Artists, to whom greatest cre∣dit

is to be given, as they have been more conversant and curious in the observati∣on hereof, then their Predecessors, do all agree not to extend three English miles in the Perpendicular G F, as is plain un∣to * 1.2 them that are acquainted with the Disputations of Tycho, Rothman, Kepler, and others. For we must here distinguish between the matter of the crepusculum, and this vaporous air, which is so little elevated above the Earth, that hardly we may live upon the tops of some hills (as Aristotle testified of Olympus) without applying a Sponge to the nostrils for want of this thick air which we use in respiration: The like doth Josephus A∣costa witness unto us of the Seres in Peru, which are hardly passable by such as labor to overcome their height; be∣cause the air, before they came to the tops of these hills, groweth so subtil and attenuated. And to add something of my own experience, my self having made some tryals of the height of the Clouds, as well in the heat of Summer, as at other times, could never yet finde them more lifted up above the super∣ficies of the Earth, then 236. perches.

Wherefore admitting G F, which is the part of the Perpendicular line that penetrateth the gross Air to be three miles, and F C, the semidiamiter of the Earth, to be 3436 miles, and the Summer and Winter heights as be∣fore; it will be manifest by suppu∣tation, that whereas K F shall pierce but four miles, or thereabouts, M F shall pass twelve, and somewhat more. So that the opposition and impe∣diment which the Sun-beams do suffer in Winter, is triple to that which they feel in their Summer passage, and doth there∣fore weaken the Suns force in that pre∣paration. And being added to the rest of the causes before specified, doth de∣monstratively prove (all together consi∣dered) that the heat in Summer excelleth that which we receive in Winter in pro∣portion, as 144. is to 1. In explaining whereof I have been the more curious, because that which is here demonstrated concerning the Suns apparition, is like∣wise to be applyed to the rest of the Planets, which moving under the same Circle that the Sun doth, shall receive the like addition or abatement of force, and

therefore of singular moment to be ob∣served in all Judgments.

Notes

• * 1.1

  Crassitude of the Air.
• * 1.2

  The depth of Vapor∣ous Air wherein we live.