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I.

DISSERTATION

CONCERNING

THE LIGHT OF THE SUN:

REFERRING TO

Vol. I. p. 33 and 130-and Vol. II. p. 420 in the
Octavo Edit.

AND TO

P. 83 and p. 620, in the Quarto Edit.

VOL. III.

B

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DISSERTATION

CONCERNING

THE LIGHT OF THE SUN.

IN further addition to what has been said, concerning the light of the Sun, in the preceding pages of the Morfels of Criticifm; and concerning the effect which the emiflion of rays of light from its body has a tendency to produce, with regard to the appearance of its magnitude, as feen by us; by whatever means or caufe thofe rays may be emitted; it may be fatisfactory to many persons to see a detail of the whole investigation, and a demonftration of all the conclufions, in a mathematical manner, upon the trueft optical principles,

Where the development of any truth, that tends to the enlargement of the human mind, is at all concerned, every means of aid is

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both useful, and neceffary;-and especially as it has been already found, by fad experience, that even mathematical proof is not always fufficient, to overcome ftrongly-riveted inveterate prejudices *.

On the prefent occafion, the clearest way will be, to begin with the fimpleft principles.

First, then :-Any point, on any surface whatever, is feen by any eye, merely because, either by emitted, or by reflected light, a ray, or rays of light proceed in every direction, ftraight from it to the eye, where-ever the eye be placed.

Therefore every point, of every vifible luminous object, muft emit rays in all directions around; as is fhewn by a section of an hemifphere of fuch rays, proceeding from the point (A) in Pl. I. Fig. 1.

2.

The whole furface, therefore, of any body, that is entirely and clearly visible, must emit entire hemifpheres of rays, extending

*This was most evidently manifefted, on the first divulgement of the fublime truths of the Newtonian Philofophy;-and is well known to thofe acquainted with the hiftory of the ftate of philofophical knowledge, in the beginning of the last century, A. D. 1700.

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