ARTICLE I.

THE COLOURS OF LIGHT.

LET the enquiry next proceed to the colours of light, to shew what they are, and what they are not. Some of the stars are white, others shining; some reddish, and others livid. Common flames, corruscations of the air, and the flame of gunpowder, are principally whitish; but the flame of sulphur beautifully blue. Some bodies also yield purple flames; but there have hitherto been discovered no green one, though the light of the glow-worm has a tendency thereto. Scarlet flames also have not been observed; but ignited iron is red, and, when intensely ignited, whitish. But all the instances of this kind are to be collected, and thrown into a table, to shew all the variety of colours in light.

ARTICLE II.

THE REFLECTIONS OF LIGHT.

LET it be next examined, what bodies reflect light, as speculums, water, polished metals, the moon, and gems. All fluid bodies, and those that have a very smooth and even surface, afford some degree of splendor, which is no other than a faint degree of light.

It must be diligently examined, whether the light of a lucid body may be reflected by another

that is lucid, as suppose ignited iron were exposed to the sun's rays: for light is reflected again and again, from speculum to speculum, though gradually fainter and weaker.

ARTICLE III.

THE MULTIPLICATIONS OF LIGHT.

LET the enquiry next descend to the multiplication of light, as by speculums, telescopes, and the like, which have a power to sharpen light, and throw it to a great distance, or else render it more subtile and better disposed for distinguishing visible objects, as we see by the practice of jewellers, and other artists, who set a spherical glass of water between the candle and their work.

It must likewise be examined, whether all bodies, when in a large quantity, do not reflect light; for it is very probable that light must pass through, or be reflected. And thus the moon, though it were an absolutely opaque body, yet might, on account of its magnitude, reflect light. Let it likewise be examined, whether the approximation of lucid bodies does not multiply light; which, in bodies that are equally lucid alike, cannot be doubted: but whether the light which is totally overpowered by a greater light, so as of itself to be rendered invisible, does not yet add some quantity of light, must be farther

examined. Even glossy bodies contribute to the increase of light: for a chamber hung with silk is lighter than when hung with cloth. Light. is also multiplied by refraction, for gems that are cut with angles, and broken glass, are more splendid than when plain or entire.

ARTICLE IV.

THE WAYS OF DROWNING LIGHT.

THE methods of drowning light should next be enquired into, as by the predominancy of a greater light the grossness or opacity of the medium, &c. Thus, the sun's rays playing upon a culinary fire, causes the flame to appear as a certain white kind of smoke. All the instances of this kind should be collected.

ARTICLE V.

THE OPERATIONS OR EFFECTS OF LIGHT.

THE operations or effects of light come next to be examined, though they seem to be but few, and have little share in bringing remarkable changes upon bodies, especially those that are solid for light, above all things, generates itself and other qualities, but sparingly; however, it certainly attenuates the air, is grateful and chearing to the spirits of animals, excites the languishing rays of colours and visible objects; for colours are nothing more than the refracted

image of light. But the particulars of this kind are to be diligently hunted up and collected.

ARTICLE VI.

THE CONTINUANCE OF LIGHT.

THE Continuance of light may be next examined, though it seems to be but momentary; for notwithstanding light has continued in a chamber many hours, it illuminates the chamber no more than it did the first moment: but the case is quite otherwise in heat, &c. for the first heat remains, and a new one is superadded thereto. The twilight is, by some, conceived to be the remains of the sun's light.

ARTICLE VII.

THE DIRECTIONS, MOTIONS, AND PASSAGES OF LIGHT.

THE directions, motions, and passages of light should be very attentively examined.Light is diffused all round; but whether at the same time it ascends a little, or is equally diffused upwards and downwards, must be enquired into. Light produces light every where about it; so when the body of a taper is not perceived through the interposition of a blind or obstacle, it still illuminates all the objects around it, excepting those that are in the shadow of the veil. And yet even these objects are somewhat illuminated by the light thrown about them; for

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an object standing within this shade may still be much better perceived than if no light at all were present; and therefore the visible body of any luminous matter, and light itself, are two very different things. Light does not penetrate fibrous bodies of an irregular and disorderly texture, though it still is not hindered by solidity and hardness as we see in glass, &c. and therefore only straight lined bodies, whose pores lie not transverse, seem capable of transmitting light.

Light is excellently transmitted through the air, which the purer it is, the better the light passes. But whether the light be conveyed by the body of the air, as sounds are by the winds, or in any other manner, should be examined, with other matters of the like kind; to complete this article.

ARTICLE VIII.

THE TRANSPARENCY OF LUMINOUS AND LUCID BODIES.

IT should next be examined, what lucid or luminous bodies are transparent. The wick of a candle is perceived thro' the flame, but objects are not visible through large bodies of flame. On the other hand, all transparency is lost in a body upon ignition, as appears in glass. The body of the air is transparent, so is water; but when these two transparent bodies are mixed together in snow or froth, they no longer preserve