354 NOVUM ORGANUM. 



cession to relieve themselves from it. The first of these explanations 

 is received by Fracastorius, and nearly all who have inquired into 

 motion with any subtlety ; and there is no doubt that the air has some 

 share in the matter ; but the other motion is undoubtedly the true one, 

 as is clear from countless experiments. Among others, we may take 

 as an Instance of the Cross the following : that a thin plate, or rather 

 stiff wire of iron, or even a reed or pen split in the middle, when 

 pressed together and bent between the finger and thumb, leaps away. 

 For it is clear that this cannot be ascribed to the air collecting behind 

 the body, since the source of motion is in the middle of the plate or 

 reed, and not in the ends. 



In like manner let the Nature investigated be that rapid and potent 

 Expansion of Gunpowder into Flame, by which such vast masses are 

 upheaved, so great weights hurled forth, as we see in the case of mines 

 and mortars. Two ways meet about this Nature after the following 

 fashion. Either the motion is excited by the mere desire of the body 

 to dilate when set on fire, or by the superadded desire of the crude 

 spirit, which flees rapidly from the fire, and bursts violently from its 

 embrace, as if from a prison. Now, the Schoolmen and common 

 opinion only busy themselves with the former kind of desire. For 

 men think that it is a fine piece of philosophy to assert that the flame 

 is, by its elementary form, endowed with a certain necessity of occu 

 pying a greater space than the body filled when it was in the form of 

 powder, and that thence arises that motion. Meanwhile, they do re 

 mark, that although this is true, if it be granted that flame is generated, 

 it is still possible that the generation of flame may be impeded by a 

 mass of matter sufficient to compress and suffocate it, so that the case 

 is not reduced to the necessity of which they speak. For they say 

 rightly that there must necessarily be expansion, and that thence 

 must follow emission or removal of the resisting body, if flame be 

 generated. But that necessity is entirely avoided if the solid 

 mass suppress the flame before it be generated. And we see 

 that flame, especially in its first generation, is soft and gentle, 

 and requires a hollow space in which to play and make trial of 

 itself. And so such violence cannot be attributed to flame by itself. 

 But the truth is, that the generation of such windy flames or, so to 

 speak, fiery winds, arises from the conflict of two bodies of entirely 

 opposite natures, the one very inflammable, which is the peculiar 

 character of sulphur, the* other dreading flame, as does the crude 

 spirit which exists in nitre; so that a marvellous conflict takes place, 

 the sulphur taking fire as quickly as possible (for the third body, the 

 willow charcoal, does scarcely anything but incorporate the other two, 

 and combine them advantageously) ; while the spirit of the nitre 

 bursts quickly forth, and at the same time expands (for it is the pro 

 perty of air and all crude bodies, and also of water, to expand by 

 heat), and by this flight and eruption meanwhile fans the flame of the 

 sulphur on all sides, as if with hidden bellows. 



Now, there may be two Instances of the Cross on this subject. The 

 one, of those bodies which are most inflammable, such as sulphur, 



