Think of anything else with the density goes down when it freezes, and think about where we would be if that wasn't the case.

想想有没有其他的物质,在降温时密度会变大，再想想如果不是这种情况,我们将会怎么样。

麻省理工公开课 - 固态化学导论课程节选

And you see that the dot intensity grows as you get closer and closer to the center.

点的密度随着到中心的距离,缩短的变密。

麻省理工公开课 - 固态化学导论课程节选