64 



COHESION. 



ice. Here you see the tin dish is frozen to the 

 board, I can even lift this little stool up by it. 



This experiment cannot, I think, fail to im- 

 press upon your minds the fact, that whenever 

 a solid body loses some of that force of attraction 

 by means of which it remains solid, heat is 

 absorbed; and if, on the other hand, we 1 convert 

 a liquid into a solid, e. g. water into ice, a cor- 

 responding amount of heat is given out. I 

 have an experiment showing this to be the 

 case. Here (Jig. 21) is a bulb, A, filled with air, 



Fig. 21. 



the tube from which dips into some coloured 

 liquid in the vessel B. And I dare say you 

 know that if I put my hand on the bulb A, and 

 warm it, the coloured liquid which is now 



