penetrability: 穿透力

identify with...: 与…等同

He identifies himself with masses.他和群众打成一片。

mass : 质量

realize=regard 看作…

volume : 体积

displace : 排出，排放，放置

Archimedes : 浮力定律，阿基米德

principle of buoyancy : 浮力定律

接下来课文...And the sensitive observer of sculpture must also learn to feel shape simply as shape, not as description or reminiscence. He must, for example, perceive an egg as a simple single solid shape, quite apart from its significance as food,or from the literary idea that it will become a bird. ...

apart from=different