1 66 POPULAR LECTURES AND ADDRESSES. 



zinc and copper beyond a certain thickness with- 

 out putting them into a condition in which they 

 lose their properties as distinct solid metals, and in 

 which, if put together, we should not find the same 

 attraction as we should calculate upon from the 

 thicker plates. I think it is impossible, con- 

 sistently with the knowledge we have of chemical 

 affinities and of the effect of melting zinc and 

 copper together, to admit that a piece of copper 

 or zinc could be divided to a thinness of much 

 less, if at all less, than i/ioo,ooo,oooth of a 

 centimetre without separating the atoms or divid- 

 ing the molecules, or doing away with the 

 composition which constitutes as a whole the 

 solid metal. In short, the constituents as it were 

 of bricks, or molecules, or atoms, of which copper 

 and zinc are built up, cannot be much, if at all, 

 less than 1/100,000, oooth of a centimetre in 

 diameter, and may be considerably greater. 



Similar conclusions result from that curious 

 and most interesting phenomenon, the soap- 

 bubble. Philosophers, old and young, who occupy 

 themselves with soap-bubbles, have one of the 



