Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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times bigger than the naked and real body: and a like or greater
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augmentation doth the image of the Sun make, which you ſee in
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that glaſs. </
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<
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>I ſay greater, for that it is more lively than the ſtar,
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as is manifeſt from our being able to behold the ſtar with much
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leſs offence, than this reflection of the glaſs. </
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<
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>The reverberation
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therefore which is to diſpere it ſelf all over this wall, cometh from
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a ſmall part of that glaſs, and that which even now came from
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the whole flat glaſs diſperſed and reſtrain'd it ſelf to a very ſmall
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part of the ſaid wall. </
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>What wonder is it then, that the firſt
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flection very lively illuminates, and that this other is almoſt
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perceptible?</
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The ſmall body of
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the ſtars fringed
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round about with
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rays, appeareth
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ry much biggerthan
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plain and naked,
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and in its native
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clarity.
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>SIMPL. </
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>I find my ſelf more perplexed than ever, and there
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preſents it ſelf unto me the other difficulty, how it can be that
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that wall, being of a matter ſo obſcure, and of a ſuperficies ſo
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poliſh'd, ſhould be able to dart from it greater light, than a glaſs
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very ſmooth and polite.</
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>SALV. </
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>Greater light it is not, but more univerſal; for as to
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the degree of brightneſs, you ſee that the reflection of that ſmall
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flat glaſs, where it beamed forth yonder under the ſhadow of the
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penthouſe, illuminateth very much; and the reſt of the wall which
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receiveth the reflection of the wall on which the glaſs is placed,
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is not in any great meaſure illuminated, as was the ſmall part on
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which the reflection of the glaſs fell. </
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>And if you would
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ſtand the whole of this buſineſs, you muſt conſider that the
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ficies of that wall's being rough, is the ſame as if it were
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ſed of innumerable ſmall ſuperficies, diſpoſed according to
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numerable diverſities of inclinations: amongſt which it
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rily happens, that there are many diſpoſed to ſend forth their
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reflex rays from them into ſuch a place, many others into another:
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and in ſum, there is not any place to which there comes not very
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many rays, reflected from very many ſmall ſuperficies, diſperſed
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throughout the whole ſuperficies of the rugged body, upon which
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the rays of the Sun fall. </
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>From which it neceſſarily
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eth, That upon any, whatſoever, part of any ſuperficies,
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oppoſed to that which receiveth the primary incident rays,
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there is produced reflex rays, and conſequently
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nation. </
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<
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>There doth alſo follow thereupon, That the ſame
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body upon which the illuminating rays fall, beheld from
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whatſoever place, appeareth all illuminated and ſhining: and
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therefore the Moon, as being of a ſuperficies rugged and
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not ſmooth, beameth forth the light of the Sun on every
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ſide, and to all beholders appeareth equally lucid. </
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<
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>But if
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the ſurface of it, being ſpherical, were alſo ſmooth as a glaſs, it
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would become wholly inviſible; foraſmuch as that ſmall part,
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from which the image of the Sun ſhould be reflected unto the eye </
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