He mentally visualizes a complex form from all round itself;
he knows while he looks at one side what the other side is like;
he identifies himself with its centre of gravity, its mass, its weight;
he realizes its volume, as the space that the shape displaces in the air.

以上4个分句，有3点疑问：
1）identify...with...  究竟是什么意思？
2）mass指的是物理学中的质量，还是艺术中的“点线面”中的“面”？
3）最后一句as...做什么成分？
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FROM 114.253.13.*