NOVUM ORGANUM 421 



motion is in the centre of the plate or pen, and not in its ex- 

 tremities. 



Again, let the required nature be the rapid and powerful mo- 

 tion of the explosion of gunpowder, by which such vast masses 

 are upheaved, and such weights discharged as we observe in 

 large mines and mortars, there are two cross-ways before us 

 with regard to this nature. This motion is excited either by 

 the mere effort of the body expanding itself when inflamed, or 

 by the assisting effort of .the crude spirit, which escapes rapidly 

 from fire, and bursts violently from the surrounding flame as 

 from a prison. The school, however, and common opinion 

 only consider the first effort ; for men think that they are great 

 philosophers when they assert that flame, from the form of the 

 element, is endowed with a kind of necessity of occupying a 

 greater space than the same body had occupied when in the 

 form of powder, and that thence proceeds the motion in ques- 

 tion. In the mean time they do not observe, that although this 

 may be true, on the supposition of flame being generated, yet 

 the generation may be impeded by a weight of sufficient force 

 to compress and suffocate it, so that no such necessity exists as 

 they assert. They are right, indeed, in imagining that the ex- 

 pansion and the consequent emission or removal of the opposing 

 body, is necessary if flame be once generated, but such a neces- 

 sity is avoided if the solid opposing mass suppress the flame 

 before it be generated ; and we in fact see that flame, especially 

 at the moment of its generation, is mild and gentle, and requires 

 a hollow space where it can play and try its force. The great 

 violence of the effect, therefore, cannot be attributed to this 

 cause ; but the truth is, that the generation of these exploding 

 flames and fiery blasts arises from the conflict of two bodies of a 

 decidedly opposite nature the one very inflammable, as is the 

 sulphur, the other having an antipathy to flame, namely, the 

 crude spirit of the nitre ; so that an extraordinary conflict takes 

 place whilst the sulphur is becoming inflamed as far as it can 

 (for the third body, the willow charcoal, merely incorporates 

 and conveniently unites the two others), and the spirit of nitre 

 is escaping, as far also as it can, and at the same time expanding 

 itself (for air, and all crude substances, and water are expanded 

 by heat), fanning thus, in every direction, the flame of the sul- 

 phur by its escape and violence, just as if by invisible bellows. 



Two kinds of instances of the cross might here be used the 

 one of very inflammable substances, such as sulphur and cam- 

 phor, naphtha and the like, and their compounds, which take 

 fire more readily and easily than gunpowder if left to themselves 

 (and this shows that the effort to catch fire does not of itself 

 luce such a prodigious effect) ; the other of substances which 

 avoid and repel flame, such as all salts ; for we see that when 



