Mother-of- Pearl and its Uses. 375 



powers to the surface, when he perceived a grooved struc- 

 ture, closely resembling, as he says, " the delicate texture of 

 the skin at the top of an infant's finger, or the minute 

 corrugations which are often seen on surfaces covered with 

 varnish or oil paint." When the mother-of-pearl was 

 regular in its structure the grooves were all parallel, and 

 the reflected images of a candle appeared all in one straight 

 line ; but when they were tortuous or curved, the images of 

 a candle were not in a straight line. 



Here, then, was proof that the colours were produced by 

 the effect of the grooves on the light reflected from the 

 surface ; for on applying the microscope to the wax, which 

 exhibited the same colours, a similar assemblage of grooves 

 was observed. A consideration of Sir Isaac Newton's 

 theory of the causes of the colours of thin bodies (which is 

 riot of a nature to be introduced here) has made it demon- 

 strable that the series of grooves breaks up a beam of 

 light which falls upon them, into a number of separate 

 parts, each of which is reflected on the eye from the 

 bottom and side of the little grooves, and assumes a par- 

 ticular colour according to the angle at which it is reflected 



This singularly beautiful appearance can be transferred 

 to balsam of Tolu, or to gum-arabic, by allowing the thin 

 film to be pressed and to solidify between two pieces of 

 mother-of-pearl ; or it may be communicated to a clean 

 surface of lead, or to the fusible metal resulting from the 

 compound of mercury and bismuth by hammering. 



With respect to the fineness and number of these 

 grooves, different specimens of shell give very different 

 results. Sometimes a magnifying power of six or eight 

 times will render them imperceptible, while in other in- 

 stances 2CXX) grooves have been counted in the space of an 

 inch, and in others, again, the number was wholly incal- 



