This week Professor E. N. da C. Andrade, F.R.S., introduces F. C. Bartlett , C.B.E., F.R.S., Professor of Experimental Psychology in the University of Cambridge, who talks about ' Psychology in Action'; and A. C. Hardy , F.R.S., Professor of Zoology in the University of Oxford, who speaks about the important food of fishes which zoologists call ' plankton '