132 CORRELATION OF THE PHYSICAL FORCES. 



rather striking when seen for the first time. I 

 have here some iron filings and gunpowder, and 

 will mix them carefully together, with as little 

 rough handling as possible; now we will, com- 

 pare the combustibility, so to speak, of the two. 

 I will pour some spirit of wine into a basin and 

 set it on fire : and, having our flame, I will 

 drop this mixture of iron filings and gunpowder 

 through it, so that both sets of particles will 

 have an equal chance of burning. And now 

 tell me which of them it is that burns? you 

 see a plentiful combustion of the iron filings; 

 but I want you to observe, that though they 

 have equal chances of burning, we shall find 

 that by far the greater part of the gunpowder 

 remains untouched ; I have only to drain off 

 this spirit of wine, and let the powder which 

 has gone through the flame dry, which it will 

 do in a few minutes, and I will then test it with 

 a lighted match. So ready is the iron to burn, 

 that it takes, under certain circumstances, even 

 less time to catch fire than gunpowder. [As 

 soon as the gunpowder was dry, Mr. Anderson 

 handed it to the Lecturer, who applied a lighted 

 match to it, when a sudden flash showed how 

 large a proportion of gunpowder had escaped 



