“How much does a ladybug weigh?” A straightforward question from a straightforward six-year old. I made a guess that seemed to satisfy. Thirty-five years later, I finally weighed a ladybug: 21 mg. I never doubted that she could walk on a ceiling or on the window where I caught her, but could she be holding on by the van derWaals forces about which I was writing? That 21 mg, plus a quick calculation, reassured me that these bugs might have learned some good physics a very long time ago. If so, what about other creatures? We are told that geckos might use these forces; their feet have hairy bottoms with contact areas like those of insects. They might put to good use forces whose appearance to us humans emerged from details in the pressures of gases, whose formulation resides in difficult theories, whose practicality is seen in paints and aerosols, and whose measurement requires delicate equipment.Were these same forces showing themselves to us during childhood summers?

The first clear evidence of forces between what were soon to be called molecules came from Johannes Diderik van der Waals' 1873 Ph.D. thesis formulation of the pressure p, volume V, and temperature T of dense gases.