dynactiˈnometer ? Obs. [f.Gr. δύν(αµις power + ἀκτίς (ἀκτῑν-) ray + µέτρον measure: see -meter, and cf. actinometer.] An instrument designed to measure the intensity of the photogenic rays, and to compute the power of object-glasses. 1851M. Claudet in Philos.Mag.