

THE SIZE OF ATOMS. 173 



monest observation on the soap-bubble shows 

 that there is no sensible diminution of contractile 

 force by reduction of the thickness to i/io,oooth 

 of a millimetre ; inasmuch as the thickness which 

 gives the first maximum brightness, round the 

 black spot seen where the film is thinnest, is 

 only about i/6oooth of a millimetre. 



The very moderate amount of work shown in 

 the preceding estimates is quite consistent with 

 this reduction. But suppose now the film to be 

 further stretched until its thickness is reduced to 

 i/io,ooo,ocoth of a millimetre (i/ioo,ooo,oooth of 

 a centimetre). The work spent in doing this is 

 one thousand times more than that which we have 

 just calculated. The heat equivalent is 570 times 

 the quantity required to raise the temperature of 

 the liquid by i Centigrade. This is far more than 

 we can admit as a possible amount of work done 

 in the extension of a liquid film. It is more 

 than the amount of work which, if spent on the 

 liquid, would convert it into vapour at ordinary 

 atmospheric pressure. The conclusion is unavoid- 

 able, that a water-film falls off greatly in its con- 



