THE KING'S MIRROR 129 



Now it must not be regarded as settled that the facts 

 are as we have just said; we have merely tried to bring 

 together and compare various opinions in order to de- 

 termine what seems most reasonable. For we see that 

 all fire originates in force. If a hard stone is stricken 

 against hard iron, fire comes out of the iron and out of 

 the energy of the stroke when they clash. You can also 

 rub pieces of wood against each other in such a way that 

 their antagonism will produce fire. It also happens fre- 

 quently that two winds rising at the same time will go 

 against each other; and when they meet in the air, heavy 

 blows fall, and these blows give forth a great fire which 

 spreads widely over the sky.* At times it also happens 

 that this fire is driven to the earth where it causes much 

 damage by burning houses and sometimes forests and 

 ships at sea. But all the fires that I have now named, 

 whether they come from iron, or winds colliding in the 

 air, or any of those mighty forces which can produce 

 fire, will consume trees, forests, and earth: while the fire 

 which we discussed earlier and which appears in Iceland 

 refuses all these things, as I have already shown. Now 

 these facts lead to this conclusion as to its nature, that 

 it is more likely to have arisen from dead things or from 

 like sources, than those other fires that we have now 

 discussed. And in case it is as we have imagined, it is 

 likely that the great earthquakes of that country origi- 

 nate in the power of those mighty fires that well through 

 the bowels of the land. 



* The common belief of medieval scientists was that lightning was caused by 

 the collision of clouds. 



