86 TOPICS OF INQUIRY 



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 burn 

 ing metals are not subtle 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 ra pid 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 disa 

 greements 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 con 

 veyed through very large spaces ; but light more swiftly, 

 as we see in cannons, where the light is sooner discerned 

 than the sound is heard, although the flame follows after. 

 Both light and sound undergo the subtlest distinctions ; 

 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 per 

 cussion ; because, if you touch the bell or chord, the sound 

 instantly ceases, from which it is evident, that the continu 

 ance 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 

 from its nearness doth also somewhat illustrate the air 

 behind the screen. But a sound excited 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 iu the case of sounds within bloodstones or when bodies 



