8. If such matter as is compounded of hard little bodies be set on fire, it must needs be, that, as they fly out in greater or less quantities, the flame which is made by them will be greater or less. And if the ethereal or fluid part of that matter fly out together with them, their motion will be the swifter, as it is in wood and other things which flame with a manifest mixture of wind. When, therefore, these hard particles by their flying out move the eye strongly, they shine bright; and a great quantity of them flying out together, they make a great shining body. For flame being nothing but an aggregate of shining particles, the greater the aggregate is, the greater and more manifest will be the flame. I have, therefore, shown a possible cause of flame. And from hence the cause appears evidently, why glass is so easily and quickly melted by the small flame of a candle blown, which will not be melted without blowing but by a very strong fire. Now, if from the same matter there be a part broken off, namely, such a part as consisteth of many of the small particles, of this is made a spark. For from the breaking off it hath a violent turning round, and from hence it shines. But though from this matter there fly neither flame nor sparks, yet some of the smallest parts of it may be carried out as far as to the superficies, and remain there as ashes; the parts whereof are so extremely small, that it cannot any longer be doubted how far nature may proceed in dividing. Lastly, though by the application of fire to this matter there fly little or nothing from it, yet there will be in the parts an endeavour to simple motion; by which the whole body will either be melted, or, which is a degree of melting, softened. For all motion has some effect upon all matter whatsoever, as has been shown at art. 3, chap. XV. Now if it be softened to such a degree, as that the stubbornness of the parts be exceeded by their gravity, then we say it is melted; otherwise, softened and made pliant and ductile. Again, the matter having in it some particles hard, others ethereal or watery; if, by the application of fire, these latter be called out, the former will thereby come to a more full contact with one another; and, consequently, will not be so easily separated; that is to say, the whole body will be made harder. And this may be the cause why the same fire makes some things soft, others hard. [Sidenote: The cause why wet hay sometimes burns of its own accord; also the cause of lightning.]