In several paper on subnormal and hyponormal operator, they cite :
P.R. Halmos, "Normal dilations and extensions of operators", Summa Brasil. Math. 2 (1950), 125-134. MR 13, 359
as a reference, but I'm having trouble finding this paper in the internet. I tried looking for the journal site, but I don't get anything . Does someone know how to find it, or can you please send it to me ?