So far, when measuring elasticities of demand, most econometricians have concentrated upon the plain elasticity of total demand for a given commodity. For many important problems we should, in addition, like to know something of "partial elasticities," as I might provisionally call them. I am thinking of the elasticity of the demand for imported units only of a given commodity; or of the elasticity of the demand, for a given good, as far as supplied by one specific country. In both cases the demand relates to part of a market only; in the first instance total sales relate to all units of the given good supplied by imports as well as by home production; in the second instance total sales consist of the sales by the country considered as well as by all competing countries.