As in geometry the most natural way of beginning is from a mathematical point, so is the same method in observations and natural history the most genuine, simple, and instructive.
大多数人死在二十或三十岁,此后他们只是自己的影子。
我们称可见光为什么?我们称之为颜色。但颜色只是我们给光碰到某物时的行为方式起的名字。