Mother'-of- Pearl and its Uses. 373 



to the manufacturer, in furnishing him with an elegant 

 material for the formation of ornamental articles of various 

 kinds. 



Mother-of-pearl is the interior laminae or scales of the 

 shell of various mollusca living in the Indian seas. The true 

 pearl oysters, as they are called, exhibit the beautifully 

 variegated colours of mother-of-pearl ; but it is a much 

 larger species called the Meleagrina margaritifera, which 

 affords the most exquisite specimens. That many shells 

 have a certain degree of resemblance on their inner sur- 

 faces to this substance we have every-day proof ; for, if we 

 inspect the interior of a common oyster shell, \ve shall 

 frequently find that it exhibits that rich play of tints which 

 constitutes the beauty of mother-of-pearl ; and, with respect 

 to mussels, Reaumur remarked, in the early part of the last 

 century, that those caught off the coast of Provence had the 

 interior of their shells variously tinted, one portion of each 

 shell being pearl-like in its appearance. 



No one can avoid being struck with the diversity 

 and delicacy of the ever-varying tints of colour of this 

 beautiful substance ; but there appears to have been no 

 attempt made to discover the cause of the production 

 until Sir David Brewster took up the subject, which he did 

 with great success, and added another to the long list of 

 services which he has rendered to optical science. 



Sir D. Brewster says : " If we take a plate of regularly 

 formed mother-of-pearl, having its two opposite surfaces 

 ground flat (but not polished), and if, with the eye placed 

 close to the plate, we view in it by reflection a candle 

 standing at the distance of a few feet, we shall observe a 

 dull and imperfect image free from colour. This image is 

 formed on the ordinary principles of reflection, and is faint 

 and undefined, owing to the imperfect reflecting power of 



