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Common flames are generally saffron-coloured, and among them celestial coruscations and the flames of gunpowder are most inclined to whiteness. The flame of sulphur is a beautiful blue. Some bodies have purple flames. No green flames are yet discovered; the most inclined thereto is the light of the glowworm. Neither are there scarlet flames. Ignited iron is reddish, and when more intensely ignited, whitish. Other instances.
V. Reflections of Light. Observe what bodies reflect light; as mirrors, waters, polished metals, the moon, and precious stones. All liquid bodies and such as have a very smooth and polished surface have some brightness; but brightness is a small degree of luminosity.
Observe carefully whether the light of one lucid body can be reflected by another; as if ignited iron be taken and exposed to the sun's rays. For the reflections of light are reflected again from mirror to mirror, though they become gradually fainter and weaker. Other instances.
VI. Multiplications of Light. Observe the multiplication of light, as by mirrors, perspective glasses, and the like, by which light may be brought to a focus, thrown to a distance, or rendered more subtle and better suited to distinguish visible objects; as we see painters place a glass of water before the candle.
Observe likewise whether all bodies when they are in large quantities do not reflect light. For light (it may be believed) either passes through or is reflected. Whence the moon, though it be an opaque body,' may yet reflect light by reason of its magnitude.
Observe likewise whether an aggregation of lucid bodies multiplies light. In the case of bodies equally lucid this cannot be doubted. But inquire whether a light which is completely overpowered by a greater light, so as to be no longer visible of itself, does not yet add some light. All bright bodies also contribute some light. A room will be lighter hung with silken stuff than with woollen. Light is multiplied likewise by refraction ; for gems that are cut in angles, and broken glass, are brighter than if they be even. Other instances.
VII. Methods of overpowering Light. Observe the methods of overpowering light; as by the superiority of a greater light, the grossness and opacity of mediums. Certainly the sun's rays directed on a flame of fire make the flame appear as a white smoke. Other instances.
VIII. Operations or Effects of Light. Observe the operations or effects of light, which are few in number and have little power to alter bodies, especially solid ones. For light above all things generates itself, but other qualities sparingly.
Light certainly somewhat attenuates the air; it is pleasant to the spirits of animals, and exhilarates them; it revives the fading rays of all colours and visible ob
1 Etiamsi fuerit corpus opacum is the reading both of Rawley's copy and Gruter’s. If it be correct, the clause must be understood as parenthetical:
whence the moon (though that indeed is an opaque body) may possibly reflect light by reason of its magnitude alone.” It seems more likely how. ever that Bacon meant to write non fuerit. - J. S.
" TOPICA INQUISITIONIS DE LUCE ET LUMINE.” 279
jects. For all colour is the broken image of light. Other instances.
IX. Continuance of Light. Observe the continuance of light, which appears to be momentary. For light, though it has continued in a room many hours, does not light it any more than if it had been there only a second; whereas in heat and other things it is otherwise. For both the former heat continues and a new one is superadded. And yet the twilight is thought by some to proceed in some degree from the remains of light.
X. Ways and Passages of Light. Observe carefully the ways and passages
of light. Light spreads all round; but inquire whether it at the same time ascend a little, or whether it spread equally upwards and downwards. Light itself generates light all round; so that when the body of light is not visible by reason of the interposition of some screen, yet the light itself illuminates all things round it, except those which lie under the shade of that screen. And even these objects are somewhat illuminated by the light diffused around; for they will be much better seen than if there were no light at all. Therefore the visible body of any lucid body and light itself seem to be different things. Light does not penetrate bodies fibrous and of an unequal texture; yet it is not hindered by the solidity of hardness, as we see in glass and the like. Therefore a straight line and pores not lying crossways alone seem to transmit light.
Light is best conveyed by the air; and the purer the air is the better does it transmit light. Inquire whether light is conveyed by the body of the air. We see certainly that sounds are conveyed by the winds, as you can hear far further with the wind than against it. But inquire whether there is anything similar in light. Other instances.
XI. Transparency of Lucid Bodies. Observe likewise the transparency of lucid bodies. The wick of a candle is seen within the flame, but through larger flames objects are not visible. Nay, on the contrary, all transparency is lost in an ignited body; as may be seen in glass, which on being ignited is no longer transparent. The body of the air is transparent, as likewise is water; but these two transparent bodies when mixed in snow or foam lose their transparency and acquire a kind of light of their own.
XII. Affinities and Oppositions of Light. Observe the affinities and also the oppositions of light. With regard to its generation, light has affinity principally with three things; heat, tenuity, and motion. Observe therefore their unions and separations with respect to light, with the degrees thereof. The flame of spirit of wine or the ignis fatuus is far gentler in heat than ignited iron, but stronger in light : glowworms, the spray of salt water, and many of the things before enumerated, throw out light, but are not hot to the touch. Ignited metals are not rare bodies, yet they have a strong heat: air, on the contrary, is one of the rarest of bodies, yet has no light. Again, air and winds are rapid in motion, but yield no light: whereas ignited metals continue sluggish in motion, and yet emit light.
" TOPICA INQUISITIONIS DE LUCE ET LUMINE.” 281
In the affinities of light which relate not to the generation, but only to the process of it, there is nothing so closely connected as sound. Observe therefore carefully with respect to their sympathies and antipathies. They agree in the following points. Light and sound diffuse themselves all round. Light and sound travel to a very great distance, but light the quickest; as we see in guns, where the light is seen before the report is heard, although the flame comes last. Light and sound admit the most subtle distinctions; witness artic
$ ulate words in the case of sound; all the images of visible things in the case of light. Light and sound scarce produce or generate anything except in the senses and spirits of animals. Light and sound are easily generated and quickly vanish. For it must not be supposed that the sound which lasts for a time after the striking of a bell or chord is produced by the first percussion. For if the bell or chord be touched and stopped, the sound dies at once. It is manifest therefore that the duration of the sound is generated by succession. Light is overpowered by a greater light, as sound by a greater sound; &c. Their differences are these : - Light as I have said
is quicker than sound. Light travels further than sound. Whether light is conveyed in the body of the air, like sound, is uncertain. Light moves only in a straight line, sound obliquely and in any way ; for when anything is seen under the shadow of a screen, it is not to be supposed that the light itself penetrates that screen, but only that it illuminates the air around it; which likewise somewhat brightens the neighbouring air behind the screen ; whereas a sound made on one side of a wall is heard without much diminution