A linear interpolation between the two, and then some numbers associated with them, 2 7-1/2 and 22-1/2. Why does he choose 7-1/2 as the freezing point of water?

两者之间做线性插值，一些数值随之标定，7。5和22。5，为什么他选择了7。5作为2,水的冰点呢？

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