512 KOVUM ORGANUM. [BOOK II. 



perhaps more bright and glorious than that reflected from the 

 body of the mooii, 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.&quot; 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 ot 

 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 ana 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, satislies itself by its axiom, that two 

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

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

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

 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 themselves 

 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 for 

 ward ; for it is clear that this cannot be attributed to the air g 

 being collected behind the body, because the source of motion ia 

 in the centre of the plate or pen, and not in its extremities. 



Again, let the required nature be the rapid and powerful 

 motion of the explosion of gunpowder, by which such vast 



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 win 

 dow in the day-time, will enable the glass to reflect distinctly for the 

 game reason, namely, that the reflected rays are not mixed rm t cou- 

 fosd &quot;w ; th those transmitted from the other side ot the window. 



