154 NOVUM ORGANUM. 



to return thither, then the presence of the earth must be 

 considered as the cause, but if it remains turned as at first 

 towards the east and west, or lose its polarity, then that 

 cause must be suspected, and farther inquiry made. 



Again, let the required nature be the corporeal substance 

 of the moon, whether it be rare, fiery, and aerial (as most 

 of the ancient philosophers have thought), or solid and 

 dense (as Gilbert and many of the moderns, with some of 

 the ancients, hold).^ The reasons for this latter opinion 

 are grounded chiefly upon this, that the moon reflects the 

 sun s rays, and that light does not appear capable of being 

 reflected, except by solids. The instances of the cross will, 

 therefore (if any), be such as to exhibit reflection by a rare 

 body, such as flame, if it be but sufficiently dense. Now 

 certainly one of the reasons of twilight is the reflection *|- of 

 the rays of the sun by the upper part of the atmosphere. 

 We see the sun s rays also reflected on fine evenings, by 

 streaks of moist clouds, with a splendour not less, but per 

 haps more bright and glorious, than that reflected from the 

 body of the moon, and yet it is not clear that those clouds 

 have formed into a dense body of water. We see also that 

 the dark air, behind the windows at night, reflects the light 

 of a candle in the same manner as a dense body would do. J 

 The experiment should also be made of causing the sun s 

 rays to fall through a hole upon some dark and bluish 

 flame. The unconfined rays of the sun, when falling on 

 faint flames, do certainly appear to deaden them, and render 

 them more like white smoke than flames. These are the 

 only instances which occur at present of the nature of those 

 of the cross, and better perhaps can be found. But it must 

 always be observed, that reflection is not to be expected 

 from flame, unless it be of some depth, for otherwise it be 

 comes nearly transparent. This at least may be considered 

 certain, that light is always either received and transmitted 

 or reflected by an even surface. 



Again, let the required nature be the motion of projectiles 

 (such as darts, arrows, and balls) through the air. The 

 school, in its usual manner, treats this very carelessly, con- 



* A sufficient proof of its necessary solidity is now afforded by the attraction 

 of the sea, and the moon s motion round the earth. 



t Rather the refraction the sky or air, however, reflects the blue rays of 

 light. 



$ The polished surface of the glass causes the reflection in this case, and not 

 the air ; and a hat or other black surface put behind the window in the day time 

 will enable the glass to reflect distinctly for the same reason ; namely, that the 

 reflected rays are not mixed and confused with those transmitted from the other 

 side of the window. 



