S4 



The second is dilatation in all solid, and rarefaction m 

 all fluid bodies. So an iron rod, the more it. is heated,, 

 increases the more in ail its dimensions. And by the 

 same degrees that it cools, it contracts, till it shrink to* 

 its first magnitude. So gold, when fused, takes up more 

 space than it did before. And mercury ascends in a, 

 hollow tube over the fire, to above thirty times its for- 

 mer height. The same degree of heat rarefies fluids 

 sooner, and hi a greater degree than it does solids. 

 And the lighter the fluid, the more it is dilated. Thus 

 air, the lightest of all fluids, expands the most. The 

 third effect of fire is motion : for in dilating bodies, it 

 must needs move their parts. All motion springs 

 from it. Only take lire away, and all nature would 

 grow into one concrete, solid as gold, and hard as dia- 

 mond. 



Pure fire needs no air to sustain it. Put calx of tin 

 into an exhausted receiver, and if you apply a burning 

 glass, the calx will be so vehemently dilated, as to break 

 the receiver into a thousand pieces. 



All the effects of elementary fire may be increased. 



1. By rubbing one body against another. And the 

 more iiard and solid the bodies are, the more heat is 

 produced. So sponges rubbed together acquire little 

 or no heat : but two pieces of iron, an intense heat, 



2. By mixing certain bodies together. So steel-filings, 

 mixed with oil of cloves, or spirit of nitre, grow exceed- 

 ing hot ; yea, burst into a violent flame. 



Yet it does not appear that any new fire is generated 

 in any of these ways. Friction does not create fire, but 

 only collect what was before dispersed. It is present 

 every where, in all bodies, in all space, at all times, and 

 that* in equal quantities. Go where you will, to the 

 highest mountain, or the deepest cavern, by" one or other 

 of these ways fire may be collected. Yea, there is no 

 place in the world, uhere the attrition of two sticks wiU 

 not make it sensible. 



But in what manner soever fire is collected, if the 

 collecting cause cease, it disappears again, unless it be 

 supplied with fuel, and iheu it becomes culinary fire. 



