60 COHESION. 



which he showed could be easily twisted about 

 with a pair of pliers.] You see, I now find no 

 difficulty in bending this end about as I like ; 

 whereas I cannot bend the cold part at all. 

 And you know how the smith takes a piece of 

 iron and heats it, in order to render it soft for 

 his purpose: he acts upon our principle of 

 lessening the adhesion of the particles, although 

 he is not exactly acquainted with the terms by 

 which we express it. 



And now we have another point to examine ; 

 and this water is again a very good substance to 

 take as an illustration (as philosophers we call 

 it all water, even though it be in the form of 

 ice or steam). Why is this water hard ? [point- 

 ing to a block of ice] because the attraction of 

 the particles to each other is sufficient to make 

 them retain their places in opposition to force 

 applied to it. But what happens when we 

 make the ice warm ? Why, in that case we 

 diminish to such a large extent the power of 

 attraction that the solid substance is destroyed 

 altogether. Let me illustrate this : I will take 

 a red-hot ball of iron [Mr. Anderson by means 

 of a pair of tongs handed to the Lecturer a red- 

 hot ball of iron, about two inches in diameter] 



