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The results of some experiments on millimeter wave and light generation by means of an undulator are described. After a brief survey of the theoretical background the design of a magnet system is discussed. An experiment is described in which a 100-Mev electron beam from the Stanford linear accelerator passed through the undulator. Light radiated by the beam was observed and the plane of polarization determined. A small linear accelerator with good bunching action was used for an experiment on millimeter wave generation. At a beam energy of 3 Mev, radiation in a wavelength band below 1.9 millimeters was observed. A peak power output of the order of one watt was obtained. Millimeter waves generated in the accelerator tube were also observed.

Individual differences were obtained in a task requiring the same-different comparison of multiobject scenes. For some Ss, performance depended only on whether the objects were in a physically plausible arrangement. It was inferred that these Ss used internalized rule systems to interrelate arrays of objects into organized scenes. For the other Ss, performance depended on whether the objects belonged together, and whether their arrangement was familiar. It was inferred that these Ss dealt with each object on an individual basis, using information concerning belongingness and familiarity of arrangement to anticipate which objects would be present and where they would be located.Recent research (De Groot, 1965;Chase & Simon, 1973) has demonstrated that chess masters are superior to amateurs in reproducing previously seen arrangements of chess pieces. The superiority, however, was obtained only when the arrangements followed the rules of chess (i.e., when they were selected from actual games); it disappeared for random arrangements of the pieces. This' finding suggested that the master's perception of the game-generated arrangements may have been guided by an internalized rule system. Relational structures based on the rule system of chess have been described by computer scientists (Michie, 1972). These structures provide schemes for interrelating arrays of chess pieces, organizing them into chunks or units. For example, an array of three pieces-a black knight, a white pawn, and a white rook-can be organized into a chunk if the array is perceived as "the rook defending the pawn that is being attacked by the knight." The use of rules to structure or organize the individual pieces into chunks could therefore be the basis for the superior reproduction performance of the chess master.Although the amateurs knew the rules of chess, their training was apparently insufficient for the knowledge to have more than a minimal influence on their performance in the reproduction task. Without a rule system for structuring the chess pieces into chunks, there was no alternative but to memorize the locations of individual pieces. As Chase and Simon (1973) conclude, the main difference between the master and amateur lies in the former's ability to organize the chess pieces into larger chunks of information.Although chess masters have intensively studied the rule system of their game, it seemed reasonable to assume that the informal experience of most normal adults is sufficient for them to master the rule system of

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