The works of Francis Bacon, lord chancellor of England.

TOPICS OF INQUIRY,
CONCERNING
LIGHT AND THE MATTER OF LIGHT.
I. Presence Tables. III. Table of Degrees.
WE have first to note which are the substances, We must remark which sorts of light are more
of whatever kind, that generate light; as stars, intense and vibrating, which less: the flame of
fiery meteors, flame, wood, metals, and other wood produces a strong light; the flame of spirit
burning bodies, sugar in scraping or breaking it, of wine, a weaker; the flame of coals when fully
the glowworm, the dews of salt water when it is kindled, a very dim and scarcely visible light.
agitated or scattered, the eyes of certain animals, IV Colours of Light
some sorts of rotten wood, large quantities of
snow; perhaps the air itself may possess a weak We have to consider the colours of light, what
light adapted to the vision of the animals which they are, what not; some stars are white, others
see by night; iron and tin, when put into aqua glittering, some red, some lead-coloured; the
fortis to be dissolved, boil, and without any fire comnmon sorts of flame are generally croceous,
produce intense heat, but whether or not they and among these the coruscations from the sky,
give out any light demands inquiry; the oil of and the sparks from flint, tend most to whiteness;
lamps sparkles in very cold weather; a kind of the flame of sulphur is ceruleous and beautiful;
faint light is sometimes observed in a clear night but in some substances are purple flames. No
around a horse that is sweating; around the hair green flames are observed: what most inclines
of certain persons, there is seen, though rarely, to greenness, is that of the glowworm. Neither
also a faint light, like a lambent flamule, as are there any crimson flames discovered: heated
occured to Lucius Marcius in Spain; there was iron is red, but if heated somewhat more intensely,
lately found an apron of a certain woman which it becomes as it were white.
was said to shine, yet only when rubbed; but it V. Reflections of Light.
had been dyed in green, of which dye alum is an
ingredient, and it rustled somewhat when shining. We have to observe what bodies reflect light:
Whether alum shines or not when scraped or as mirrors, water, polished metals, the moon,
broken is matter of inquiry; but, I suppose, it precious stones. All liquid bodies and such as
requires more violent breaking, because it is firmer have very equal smooth surfaces are somewhat
than sugar. In like manner, some stockings bright; but brightness is a certain small degree
shine whilst you are pulling them off, whether of light.
from sweat or the dye of alum. We have to remark attentively, whether or not
the light of one lucid body can be reflected by
II..ilbsence Tables. another lucid body; as if you took heated iron and
opposed it to the sun's rays. For the reflections
We must also observe which are the substances of light are reflected on, yet becoming gradually
that give no light, yet have much similitude to feebler, from mirror to mirror.
such as do produce it. Boiling water does not
VI. Multiplication of Light.
give light; air though unusually heated does not
give light; mirrors and diamonds, which so The multiplication of light must next be constrikingly reflect light, give no light of their own. sidered: as by mirrors, perspectives, and the like,
In this kind of instances we have also to con- by which light may be sharpened and thrown to
sider diligently the instances migratory, namely, a distance, or also rendered subtler and softer for
when light, as if transient, is present, and when distinguishing visible objects; as you may see
absent. A burning coal gives light, but loses it among painters, who use a phial filled with water
instantly when strongly compressed; the crystal- beside their candle.
line humour of the glowworm, after the worm's Whether all bodies of any considerable size do
death, even when broken and divided into parts, not reflect light, must also be considered. For
retains light for a short time, which, however, light, as may be believed, either goes through or
soon after fades away is reflected: from which cause the moon, though
452