Studies of iridescent colour, and the structure producing it.— II. Mother-of-pearl

The structure giving rise to the colour of mother-of-pearl is investigated. The results generally are confirmatory of those given by Brewster and A. H. Pfund. Micro-photographs are reproduced showing the grating structure of a pearl-oyster shell, and the structure of parallel layers of an “ear” shell. The absorption spectrum of the latter is also reproduced. In agreement with the observed spacing of the layers under the microscope, it shows the reflexion to be of the second order.