420 BACON 



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 ex- 

 hibit reflection by a rare body, such as flame, if it be but suffi- 

 ciently 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 even- 

 ings by streaks of moist clouds, with a splendor not less, but 

 perhaps 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. 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 ex- 

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

 becomes 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, considering it 

 enough to distinguish it by the name of violent motion, from 

 that which they term natural, and as far as regards the first 

 percussion or impulse, satisfies itself by its axiom, that two 

 bodies cannot exist in one place, or there would be a penetration 

 of dimensions. With regard to this nature we have these two 

 cross-ways : The motion must arise either from the air carry- 

 ing the projected body, and collecting behind it, like a stream 

 behind boats, or the wind behind straws ; or from the parts of 

 the body itself not supporting the impression, but pushing them- 

 selves forward in succession to ease it. Fracastorius, and nearly 

 all those who have entered into any refined inquiry upon the 

 subject, adopt the first. Nor can it be doubted that the air has 

 some effect, yet the other motion is without doubt real, as is 

 clear from a vast number of experiments. Amongst others we 

 may take this instance of the cross, namely, that a thin plate or 

 wire of iron rather stiff, or even a reed or pen split in two, when 

 drawn up and bent between the finger and thumb, will leap 

 forward; for it is clear that this cannot be attributed to fhe 

 air being collected behind the body, because the source of 



