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Modern experimenters have succeeded by direct experiments in placing
in evidence this heterogeneous character of matter when taken in small
mass. Thus, for example, the superficial tension, which is constant
for the same liquid at a given temperature, no longer has the same
value when the thickness of the layer of liquid becomes extremely
small. Newton noticed even in his time that a dark zone is seen to
form on a soap bubble at the moment when it becomes so thin that it
must burst. Professor Reinold and Sir Arthur Ruecker have shown that
this zone is no longer exactly spherical; and from this we must
conclude that the superficial tension, constant for all thicknesses
above a certain limit, commences to vary when the thickness falls
below a critical value, which these authors estimate, on optical
grounds, at about fifty millionths of a millimetre.
From experiments on capillarity, Prof. Quincke has obtained similar
results with regard to layers of solids. But it is not only capillary
properties which allow this characteristic to be revealed.


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