40 FARADAY 



to you by pouring it over this bulb; there! it is becoming 

 solid; and look at the colored liquid, how it is being driven 

 down the tube, and how it is bubbling out through the water 

 at the end; and so we learn this beautiful law of our 

 philosophy, that whenever we diminish the attraction of 

 cohesion we absorb heat, and whenever we increase that 

 attraction heat is evolved. This, then, is a great step in 

 advance, for you have learned a great deal in addition to 

 the mere circumstance that particles attract each other. But 

 you must not now suppose that because they are liquid they 

 have lost their attraction of cohesion; for here is the fluid 

 mercury, and if I pour it from one vessel into another, I find 

 that it will form a stream from the bottle down to the 

 glass a continuous rod of fluid mercury, the particles of 

 which have attraction 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 

 experiment with soap-bubbles, to take care to have every 

 thing clean and soapy). I will now blow a bubble, and that 

 I may be able to talk and blow a bubble too, I will take a plate 

 with a little of the soapsuds in it, and will just soap the 

 edges of the pipe and blow a bubble on to the plate. Now 

 there is our bubble. Why does it hold together in this 

 manner? Why, because the water of which it is composed 

 has an attraction of particle for particle so great, indeed, 

 that it gives to this bubble the very power of an India-rubber 



