On Certain Metric Spaces Arising From Euclidean Spaces by a Change of Metric and Their Imbedding in Hilbert Space

I. J. Schoenberg, On Certain Metric Spaces Arising From Euclidean Spaces by a Change of Metric and Their Imbedding in Hilbert Space, Annals of Mathematics, Second Series, Vol. 38, No. 4 (Oct., 1937), pp. 787-793