Contact Electricity of Metals. 109 



intends, in continuance of his investigation, to determine as 

 accurately as he can the heats of combination of many different 

 alloys of zinc and copper and of silver and copper, and so to 

 find whether or not it is greatest when the proportions are 

 exactly the chemically " combining proportions." He hopes 

 also to make similar experiments with bismuth and antimony, 

 using aqua regia as solvent.] 



[§ 32. February^ 1898. — Looking now to column 5 of the 

 table of § 27, we see from Professor Boherts- Austen's result, 

 36 thermal units, for the heat of combination of SO per cent, 

 copper with 70 per cent, zinc, and from Gait's 77 thermal 

 units for equal parts of copper and zinc, that the law of 

 electric action on which the calculations of the tables are 

 founded is utterly disproved for discs of metal of one one- 

 thousand-millionth of a centimetre thickness, with air or sether 

 spaces between them of the same thickness, but is not dis- 

 proved for thicknesses of one one-hundred-millionth of a 

 centimetre. 



Consider now our ideal insulated pile (§ 29) of discs 10~ 8 

 of a centimetre thick, with air or aather spaces of the same 

 thickness between them. Suddenly establish metallic con- 

 nexion between all the discs. The consequent electric 

 currents will generate 7*4 thermal units, and heat the disks by 

 79° 0. Take again the insulated column with thicknesses 

 and distances of 10~~ s of a centimetre ; remove the ideal glass 

 separators and diminish the distance to 10 -9 of a centimetre 

 (the thicknesses of discs being still 10 -8 of a centimetre). 

 Now, with these smaller distances between two opposed areas, 

 make metallic contact throughout the column by bending the 

 corners (the discs for convenience being now supposed 

 square) : 74 thermal units will be immediately generated, 

 and the discs will rise 790° in temperature, and we have a 

 column of hot brass — perhaps solid, perhaps liquid. This last 

 statement assumes that the law of electric action, on which 

 the table is founded, holds for discs 10 -8 of a centimetre 

 thick, with aether or air spaces between them of 10 -9 of a centi- 

 metre. In reality it is probable that the law of electric action 

 for discs 10 ~ 8 of a centimentre thick, begins to merge into 

 more complicated results of intermolecular forces, before 

 the distance is as small as 10 -8 of a centimetre. 



Resuming our mental molecular microscopic binocular 

 (§16, footnote), we cannot avoid seeing molecular structures 

 beginning to be perceptible at distances of the hundred- 

 millionth of a centimetre, and we may consider it as highly 

 probable that the distance from any point in a molecule of 

 copper or zinc to the nearest corresponding point of another 



