Abstract
It is found that Wood anomalies of intensity distribution in grating spectra are frequently developed by coating the grating with an evaporated film of magnesium, silver or aluminum. It is observed that the effect is best exhibited by gratings with very narrow fine ruling. The typical band illustrating the phenomenon is a double band—a dark band in juxtaposition to, and on the red side of a bright band. The dark band is characterized by a sharp boundary on the blue side. The Rayleigh formula which predicts the position of these anomalies in the spectrum was found to hold for the measurements on this sharp boundary. An empirical relation of similar form is developed from measurements on the bright bands. Other general observations on the bands are recorded.

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