246 THE SCHOOL OP REAUMUR 



the singular substance which gives a lustre to the scales 

 of fishes, and this led him to study the development and 

 growth of the scales themselves. These inquiries became 

 linked to researches which he had carried on ever since 

 1709, into the formation and growth of the shells of 

 moUusks, which he showed not to arise by intussuscep- 

 tion [or incorporation of new matter with every part of 

 a pre-existing structure ; Reaumur maintained that the 

 shell grows by the addition of layers]. In 1717 he 

 attended to pearl-formation, and sought to compel bi- 

 valves to produce pearls. When he had occasion, in 

 1715, to describe the turquoise mines of the south of 

 France, and the methods in use for producing the blue 

 colour, he discovered that turquoises are the teeth of the 

 large [extinct] animal, since described under the name of 

 mastodon [this is true only of the so-called occidental 

 turquoise, which forms on teeth and bones after long 

 burial in the ground]. But his most important researches 

 in technical science were those upon iron and steel, 

 published as a separate work in 1722 under the 

 title Traite sur Vart de convertir le fer en acier, et 

 d'adoucir le fer fondu. Our forges were then almost 

 in their infancy, and we made no steel ; all that was 

 required in the arts was brought to us from abroad. It 

 was only by innumerable experiments that E^aumur 

 came to discover the art of steel-making. The Duke of 

 Orleans, then Regent of France, proposed to remunerate 

 him for this service by a pension of twelve thousand 

 livres. At this date no tin-plate was made in France ; 

 all came to us from Germany ; Reaumur succeeded in 

 making it by a cheap method, which he published in 

 1725. In his numerous experiments he had more than 

 once occasion to remark that cast metals, in cooling, 

 assumed regular forms; and this led him in 1724 to 



