42 COHESION. 



row morning we shall have a great deal of the 

 alum crystallised out, that is to say, come back 

 to the solid form. [The Lecturer here poured 

 a little of the hot solution of alum into the 

 glass dish, and when the latter had thus been 

 made warm, the remainder of the solution was 

 added.] I am now doing that which I advise 

 you to do if you use a glass vessel, namely 4 - 

 warming it slowly and gradually, and in repeat- 

 ing this experiment do as I do, pour the liquid 

 out gently, leaving all the dirt behind in the 

 basin ; and remember that the more carefully 

 and quietly you make this experiment at home, 

 the better the crystals. To-morrow you will 

 see the particles of alum drawn together, and 

 if I put two pieces of coke in some part of the 

 solution (the coke ought first to be washed very 

 clean, and dried), you will find to-morrow that 

 we shall have a beautiful crystallisation over 

 the coke, making it exactly resemble a natural 

 mineral. 



Now how curiously our ideas expand by 

 watching these conditions of the attraction of 

 cohesion ! -how many new phenomena it gives 

 us beyond those of the attraction of gravitation ! 

 See how it gives us great strength. The things 



