The Surface Strength of Glass and other Materials

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It would appear that in any ordinary method of testing, we measure, in Littleton's words, “not the strength of the glass, but the weakness of its surface.” This agrees also with A. A. Griffith's conclusion, that, theoretically (by calculations from thermal data), the strength of glass ought to be in the region of 1,000,000 lb.fsq. in, whereas we cannot trust the average window-pane to withstand 10,000 lb.fsq. in.

F. W. Preston