I've been reading some early physics. Here's Huygens noting that even hard objects are springy - and then he uses this to make speculations about the particles that make up the luminiferous ether:
"For I have found that on striking with a ball of glass or of agate against a large and quite thick piece of the same substance which had a flat surface, slightly soiled with breath or in some other way, there remained round marks, of smaller or larger size according as the blow had been weak or strong. This makes it evident that these substances yield where they meet, and spring back: and for this time must be required."
