ADVANCEMENT OF LEARNING 209 



alone to give light; and that water and air are not utter 

 enemies thereto, appear from the dashing of salt water in 

 a dark night, and a hot season, when the small drops of 

 the water, struck off by the motion of the oars in rowing, 

 seem sparkling and luminous. We have the same ap 

 pearance in the agitated froth of the sea, called sea-lungs. 

 And, indeed, it should be inquired what affinity flame and 

 ignited bodies have with glow-worms, the Luciola, the In 

 dian fly, which casts a light over a whole room; the eyes 

 of certain creatures in the dark; loaf-sugar in scraping or 

 breaking; the sweat of a horse bard ridden, etc. Men 

 have understood so little of this matter, that most imagine 

 the sparks, struck between a flint and steel, to be air in at 

 trition. But since the air ignites not with heat, yet appar 

 ently conceives light, whence owls, cats, and many other 

 creatures see in the night (for there is no vision without 

 light), there must be a native light in air; which, though 

 weak and feeble, is proportioned to the visual organs of 

 such creatures, so as to suffice them for sight. The error, 

 as in most other cases, lies here, that men have not de 

 duced the common forms of things from particular in 

 stances, which is what we make the proper business of 

 metaphysics. Therefore let inquiry be made into the 

 form and origins of light; and, in the meantime, we set 

 it down as deficient. And so much for the doctrine of the 

 substance of the soul, both rational and sensitive, with its 

 faculties, and the appendages of this doctrine. 



