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>fr. Iiay. These dimensions, as stated previously, were for pillars under normal conditions, and were intended to be set out in plan, from the exterior points of the structure to be protected.He feared, however, the citing of all cases during his experience, upon which the formula was founded, would not only occupy much space, but would need many illustrations t o show in an instructive manner the precise elements of each case. Having regard to the fact that the formula had met with general acceptance, he would suggest it to be taken as embodying all he could show in such an appendix. In conclusion, he considered the question of support to be one requiring all the skill and prudence of the mining engineer to determine, combined with experience in the investigation of the effects of subsidence both in their geological and physical aspects, and in the observance of any accompanying conditions which might tend to mitigate or exaggerate the risk of injury to the surface.

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