The System of RX Cassiopeiae.

The Harvard photographic observations of RX Cassiopeiae are discussed in detail. The principal con- clusions relative to this unusual system are: (1) there is a regular intrinsic variation in a period of 517 days, and this may be ascribed to variation of the blue component with a range of 0.6 mag.; (2) the photometric elements of the eclipsing pair, derived at the times of the maximum, mean, and minimum of the long- period curve, are sensibly similar, except in the ratios of surface brightness; and (3) the relative lumi- nosities of the components, derived from the, long-period variations and from the photometric elements, are in agreement