1883.] on the Size of Atoms. 191 



raise the temperature of the material by 62°. This is barely, if 

 at all, admissible, according to our present knowledge, or, rather, 

 want of knowledge, regarding the heat of combination of zinc and 

 copper. But suppose the metal plates and intervening spaces to 

 be made yet four times thinner, that is to say, the thickness of each 

 to be l-400,000,000th of a centimetre. The work and its heat 

 equivalent will be increased sixteenfold. It would therefore be 990 

 times as much as that required to warm the mass by one degree 

 Centigrade, which is very much more than can possibly be produced 

 by zinc and copper in entering into molecular combination. Were 

 there in reality anything like so much heat of combination as this, a 

 mixture of zinc and copper powders would, if melted in any one spot, 

 run together, generating more than heat enough to melt each through- 

 out ; just as a large quantity of gunpowder if ignited in any one spot 

 burns throughout without fresh application of heat. Hence plates of 

 zinc and copper of 1-300,000, 000th of a centimetre thick, placed close 

 together alternately, form a near approximation to a chemical combina- 

 tion, if indeed such thin plates could be made without splitting atoms." 

 In making brass, if we mix zinc and copper together we find no 

 very manifest signs of chemical affinity at all ; there is not a great 

 deal of heat developed ; the mixture does not become warm, it does not 

 explode. Hence we can infer certainly that contact-electricity action 

 ceases, or does not go on increasing according to the same law, when 

 the metals are subdivided to something like l-100,000,000tli of a 

 centimetre. Now this is an exceedingly important argument. I have 

 more decided data as to the actual magnitude of atoms or molecules 

 to bring before you presently, but I have nothing more decided in 

 giving for certain a limit to supposahle smallness. We cannot reduce 

 zinc and copper beyond a certain thickness without putting them into 

 a condition in which they lose their properties as wholes, 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 im- 

 possible, consistently 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 1-1 00,000,000th of a centimetre without sepa- 

 rating the atoms or dividing the molecules, or doing away with the 

 composition which constitutes as a whole the solid metal. In short, 

 the structure 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, 000,000th of a centimetre in diameter, and maybe 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 most interesting 

 subjects of physical science to admire. Blow a soap-bubble and look 

 at it, — you may study all your life perhaps, and still learn lessons in 

 physical science from it. You will now see on the screen the image 

 Vol. X. (No. 76.) o 



