TOPICS OF INQUIRY CONCERNING LIGHT.
it be an opaque body, may yet reflect light by 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 spi rits 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 Light. 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 ight at all were present. Thus the visible body 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 ubstance, 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 Sadies. We must also inquire respecting the transpa rency of lucid bodies. The wick of a candle is seen within the flame; but through larger flames objects reach not the sight. But again, all trans parency is lost on heating any body, as may be seen in glass, which is no longer transparent when heated. The substance of air is transpa rent, also of water; yet, these two transparent substances when mixed, as in snow or foam, are 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. W T e must, therefore, consider the marriages and divorces of these three with light, also the degrees of these same marriages and divorces. The flame of spirit of wine or of an ignis fatuus, has a much feebler 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 out light, yet are not hot to the touch. Also 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 progres sion, 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
