66 COHESION. 



of fluid mercury, the particles of which have at- 

 traction sufficient to make them hold together 

 all the way through the air down to the glass 

 itself: and if I pour water quietly from a jug, 

 I can cause it to run in a continuous stream in 

 the same manner. Again, let me put a little 

 water on this piece of plate glass, and then 

 take another plate of glass and put it on the 

 water; there ! the upper plate is quite free to 

 move, gliding about on the lower one from side 

 to side ; and yet, if I take hold of the upper 

 plate and lift it up straight, the cohesion is so 

 great that the lower one is held up by it. See 

 how it runs about as I move the upper one, and 

 this is all owing to the strong attraction of the 

 particles of the water. Let me show you 

 another experiment. If I take a little soap and 

 water not that the soap makes the particles 

 of the water more adhesive one for the other, 

 but it certainly has the power of continuing in 

 a better manner the attraction of the particles 

 (and let me advise you when about to experi- 

 ment with soap-bubbles to take care to have 

 everything clean and soapy). I will now blow 

 a bubble, and that 1 may be able to talk and 

 blow a bubble too, I will take a plate with a 



