TOPICS OF INQUIRY, CONCERNING LIGHT AND THE MATTER OF LIGHT. I. Presence Tables. WE have first to note which are the substances, of whatever kind, that generate light; as stars, fiery meteors, flame, wood, metals, and other burning bodies, sugar in scraping or breaking it, the glowworm, the dews of salt water when it is agitated or scattered, the eyes of certain animals, some sorts of rotten wood, large quantities of snow; perhaps the air itself may possess a weak light adapted to the vision of the animals which see by night; iron and tin, when put into aqua fortis to be dissolved, boil, and without any fire produce intense heat, but whether or not they give out any light demands inquiry; the oil of lamps sparkles in very cold weather; a kind of faint light is sometimes observed in a clear night around a horse that is sweating; around the hair | of certain persons, there is seen, though rarely, also a faint light, like a lambent flamule, as occured to Lucius Marcius in Spain; there was lately found an apron of a certain woman which was said to shine, yet only when rubbed; but it had been dyed in green, of which dye alum is an ingredient, and it rustled somewhat when shining. Whether alum shines or not when scraped or broken is matter of inquiry; but, I suppose, it requires more violent breaking, because it is firmer than sugar. In like manner, some stockings shine whilst you are pulling them off, whether from sweat or the dye of alum. II. Absence Tables. We must also observe which are the substances that give no light, yet have much similitude to such as do produce it. Boiling water does not give light; air though unusually heated does not give light; mirrors and diamonds, which so strikingly reflect light, give no light of their own. In this kind of instances we have also to consider diligently the instances migratory, namely, when light, as if transient, is present, and when absent. A burning coal gives light, but loses it instantly when strongly compressed; the crystalline humour of the glowworm, after the worm's death, even when broken and divided into parts, retains light for a short time, which, however, soon after fades away III. Table of Degrees. We must remark which sorts of light are more intense and vibrating, which less: the flame of wood produces a strong light; the flame of spirit of wine, a weaker; the flame of coals when fully kindled, a very dim and scarcely visible light. IV. Colours of Light. We have to consider the colours of light, what they are, what not; some stars are white, others glittering, some red, some lead-coloured; the common sorts of flame are generally croceous, and among these the coruscations from the sky, and the sparks from flint, tend most to whiteness; the flame of sulphur is ceruleous and beautiful; but in some substances are purple flames. No green flames are observed: what most inclines to greenness, is that of the glowworm. Neither are there any crimson flames discovered: heated iron is red, but if heated somewhat more intensely, it becomes as it were white. V. Reflections of Light. We have to observe what bodies reflect light: as mirrors, water, polished metals, the moon, precious stones. All liquid bodies and such as have very equal smooth surfaces are somewhat bright; but brightness is a certain small degree of light. We have to remark attentively, whether or not the light of one lucid body can be reflected by another lucid body; as if you took heated iron and opposed it to the sun's rays. For the reflections of light are reflected on, yet becoming gradually feebler, from mirror to mirror. VI. Multiplication of Light. The multiplication of light must next be considered: as by mirrors, perspectives, and the like, by which light may be sharpened and thrown to a distance, or also rendered subtler and softer for distinguishing visible objects; as you may see among painters, who use a phial filled with water beside their candle. Whether all bodies of any considerable size do not reflect light, must also be considered. For light, as may be believed, either goes through or is reflected: from which cause the moon, though it be an opaque body, may yet reflect light by light at all were present. Thus the visible body reason of its magnitude. We must ascertain, too, whether or not the aggregation of lucid bodies multiplies light. And in regard to bodies equally lucid there is no doubt of this but it remains for inquiry, whether or not a light, which is evidently overcome and rendered of itself invisible by a greater light, doth not yet add some light. Whatsoever is bright also contributes somewhat of light, for an apartment is much lighter when hung with silk than with cloth. Light is also multiplied by refraction; for gems when cut into angles, and glass when broken, shine much more than if they were smooth. VII. Modes of destroying Light. The modes of destroying light must also be remarked as by the exuberance of greater light, and by dense and opaque mediums. The sun's rays certainly, falling on the flame of a fire, make the flame seem like a kind of whiter smoke. VIII. Operations or Effects of Light. We have to consider the operations or effects of light, which, it seems, are few, and possess little power of changing bodies, especially solids. Light above all things generates itself, other qualities sparingly. Light doth certainly in some measure attenuate the air, is grateful to the spirits of animals, and exhilirates them; it excites the slumbering rays of all colours and visible things, for every colour is the broken image of light. IX. Continuance of Light. The continuance of light must be investigated; which, as it appears, is momentary. For light doth not illuminate an apartment more when it hath continued there for many hours, than for any single moment; which is not so in respect of heat, &c.; for the first portion of heat remains, and a new one is added to it. Yet, twilight is by some thought to arise from the traces of the sun. X. Ways and Progress of Lagnt. We have attentively to consider the ways and progress of light. Light is shed around on all sides; but it remains for inquiry whether it at the same time ascends a little, or is equally shed around, upwards, and downwards. The light itself generates light everywhere around it; so that when the body of light, on interposing a screen, is not discerned, yet the light itself illuminates every thing around, except the objects which fall within the shadow of the screen: these, however, receive some light from the light which is thrown around; for any thing within the shadow of the screen can be discerned much better than if no of any lucid object, and the light itself, seem to be things different. Light doth not penetrate bodies which are fibrous and of unequal structure; but yet is not impeded by the solid hardness of a substance, as you shall see in glass and the like. Thus the straight line and the pores which are not transverse, alone seem to transmit light. The best conductor of light is air, which conveys light the better the purer it is. It remains for inquiry whether or not light is carried through the body of the air. Sounds certainly we see carried by winds, so that they may be heard farther when going with the wind than against it. But it remains for inquiry whether or not any thing of the kind takes place with light. XI. Transparency of Lucid Bodies. We must also inquire respecting the transparency of lucid bodies. The wick of a candle is seen within the flame; but through larger flaines objects reach not the sight. But again, all transparency is lost on heating any body, as may be seen in glass, which is no longer transparent when heated. The substance of air is transpasubstances when mixed, as in snow or foam, are rent, also of water; yet, these two transparent no longer transparent, but acquire a certain light of their own. XII. Cognations and Hostilities of Light. The cognations, and also the hostilities of light must be investigated. Light, as far as regards its production, has most of all cognation with three things, heat, tenuity, and motion. We must, these three with light, also the degrees of these therefore, consider the marriages and divorces of of wine or of an ignis fatuus, has a much feebler same marriages and divorces. The flame of spirit heat than red-hot iron, but a stronger light. Glowworms, and the dews of salt water, and many of the things which we mentioned, throw Also out light, yet are not hot to the touch. burning metals are not subtile bodies, but yet they have an ardent heat. But, on the other hand, air is one of the subtlest bodies, yet it is void of light; again, this same air, and also winds, though rapid in motion, afford no light. But, on the other hand, burning metals do not lay aside their sluggish motion, nevertheless vibrate light. But in the cognations of light, which have no relation to its production, but only to its progression, nothing is so much allied to it as sound. To the sympathies and disagreements of the two we must therefore strictly direct our attention. In the following they agree: both light and sound are diffused around on all sides. Light and sound are conveyed through very large spaces; but light more swiftly, as we see in can nons, where the light is sooner discerned than the on one side of a wall is heard on the other side not much weaker. Sound also is heard within the septa of solid bodies, though fainter, as in the case of sounds within bloodstones; or when bodies are struck under water. But light is not at all visible in a solid, opaque body, which is close on all sides. Light penetrates deeper than sound, as at the bottom of waters. Every sound is produced in the motion and manifest collision of bodies: not so light. sound is heard, although the flame follows after. | from its nearness, doth also somewhat illustrate Both light and sound undergo the subtlest dis- the air behind the screen. But a sound excited tinctions; as sounds in words articulate, and light in the images of all visible objects. Light and sound produce, or generate almost nothing, except in the senses and spirits of animals. Light and sound are easily generated, and soon fade away. For there is no cause why any one should conceive that the sound, which continues for some time after a bell or chord has been struck, is produced at the moment of percussion; because, if you touch the bell or chord, the sound instantly ceases, from which it is evident, that the continuance of the sound is created by succession. One light is destroyed by a greater, as one sound by a greater, &c. But light and sound differ, in that light, as observed, is more rapid than sound, and goes over larger spaces: whether or not light is conveyed in the body of the air, in the same manner as sound, is uncertain: light proceeds in straight lines only, but sound in crooked lines, and in all directions. For where any thing is discerned in the shadow of a screen, there is no cause to think that the light penetrates the screen, but only that it illuminates the air around, which, But hostilities of light, or privations, if any like the term better, occur not. However, as is exceedingly probable, the torpor of bodies, in their parts, is very inimical to light. For almost nothing gives light that is not in its own nature remarkably mobile, or excited by heat, or motion, or vital spirit. Yet I always mean, that not only other instances remain to be investigated, (for these few we have adduced only by way of example,) but also that new topical articles, as the nature of things requires, may be added. FRANCIS BACON'S APHORISMS AND ADVICES CONCERNING THE HELPS OF THE MIND AND THE KINDLING OF NATURAL LIGHT. MAN, the servant and interpreter of nature, does | him, who can induce an effect upon certain suband understands as much as he has actually or stances only of such as are susceptible, is likementally observed of the order of nature: he wise imperfect. neither knows nor can do more. The naked hand of man, however strong and constant, suffices for but few operations, and those easy; the same, by help of instruments, performs many and obstinate operations: so is it also with the mind. The instruments of the hand excite or direct motion: and the instruments of the mind prompt or caution the intellect. On a given basis of matter to impose any nature, within the limits of possibility, is the intention of human power. In like manner, to know the causes of a given effect, in whatever subject, is the intention of human knowledge: which intentions coincide. For that which is in contemplation as a cause, is in operation as a medium. The knowledge of him who knows the cause of any nature, as of whiteness or of heat, in certain subjects only, is imperfect. And the power of He who knows the causes of any nature in some subjects only, knows the efficient or materiate cause, which causes are inconstant, and nothing else but vehicles and causes conveying form. But he who comprehends the unity of nature in the most dissimilar substances, knows the form of things. He who knows the efficient and materiate causes, composes or divides things previously invented, or transfers and produces them; also in matter somewhat similar, he attaineth unto new inventions; the more deeply fixed limits of things he moveth not. He who knows the forms, discloses and educes things which have not hitherto been done, such as neither the vicissitudes of nature, nor the diligence of experience might ever have brought into action, or as might not have entered into man's thoughts. The same is the way and the perfection of truth | light belongs not to the form of heat, it is the and of power: this, namely, to discover the forms same as if you were to say, in producing heat it of things, from the knowledge of which followeth is not necessary to produce light also. true contemplation and free operation. (The rest were not finished.) Nor do these proceed under our authority. Thou, O Father, turning to the works which thy hands made, saw that all things were very good; but man, turning to the works which his hands made, saw that all was vanity and vexation of spirit. Therefore, if we have laboured amid thy works, thou wilt make us partakers of thy gratulation and of thy Sabbath. We humbly entreat that this disposition may abide in us; and that by our hands the human family may be endowed with new alms from thee. These we The contemplative and the operative utterance commend to thy eternal love, through our Jesus, of words differ not in reality. For when you say, thy Christ, God with us. J. A. C. The discovery of forms which proceeds by the Lexclusion or rejection of natures is simple and one. For all natures, which are absent in a given present nature, or present in a given absent nature, pertain not to form; and, after complete rejection or negation, the form and affirmation remains. If you inquire, for example, into the form of heat, and find water hot, yet not lucid, reject light: if you find air thin, yet not hot, reject tenuity. This is short to say, but it is reached by a long circuit. THE END OF VOL. I. |