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160 so there are no changes of temperature suffered by our standard between the time when we measure its length in wave lengths and the time when we stop off its length for comparison with, or verification of some other standards.

Mr. Eisenmann: In measuring the base of the Lake Survey, of course we worked in all seasons, so that we were subject to great changes of temperature. When we brought our work into the operating room we found that even the thermometers had a set in the glass.

Mr. Whitelaw: Would not glass be better than metal for your standards?

Prof. Morley: We tried glass first, but the artists did not succeed in making the surface plane, and we tried metal.