"The best way to prove that when one body pushes another it does not touch it, is to measure the distance between... Here are two glass lenses, one of which is pressed against another... By means of an electric light... a series of coloured rings is formed on the screen... first observed and first explained by Newton. The particular colour of any ring depends on the distance between the surfaces... [W]hat we call optical contact is not real contact. Optical contact indicates only that the distance between... is much less than a wavelength... Now it is possible to bring two pieces of glass so close together, that... they will adhere together so firmly, that when torn asunder the glass will break... Thus... bodies begin to press against each other whilst still at a measurable distance, and that even when pressed together with great force they are not in absolute contact... Why, then, say the advocates... should we continue to maintain the doctrine, founded only in the rough experience of a pre-scientific age, that matter cannot act where it is not, instead of admitting that all... contact essential to action were in reality cases of action at a distance... too small to be measured..."