1 D.H. Crandall, G.H. Dunn, A.C. Gallagher, D.G. Hummer, C.V. Kunasz, D.A. Leep, and P.O. Taylor, Astrophysical Journal 191, (1974).
1 P.O. Taylor, K.T. Dolder, W.E. Kauppila, and G.H. Dunn, Review of Scientific Instruments 45, (1974).