flicted with it is the materials containing the largest number of air he does observe a difference. cells or dead air spaces that give the most efficient In case a totally color-blind man wishes to distin- results as non-conductors of heat. Durability is also guish slightly differing shades of… … really green pended on secrecy brighter than to make it profit- with the naked able. The usual eye, while red objects seen by him through the same result of such practice followed. Two of the em- green glass will appear to be darker than when viewed can: distinguish twelve different shades. In this…
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