REAUMUR. 185 



inhabitant of fresh water, and about six inelies in 

 length. This silvery ingredient is procured by ma- 

 cerating its scales in water, and is then mixed with 

 a little isinglass. The small globes which are to re- 

 present pearls are first furnished with an internal 

 coating of the solution, and then filled with melted 

 wax to give them suitable weight. The pearly mat- 

 ter occurs also in the membrane which envelopes 

 the stomach and intestines, and is supposed by 

 Reaumur to be produced in the latter, from which 

 it is conveyed by the blood-vessels to the scales. 

 He likewise made inquiries into the formation and 

 growth of shells, which he proved to be developed 

 by accessions to their outer edge. He is even said 

 to have examined the structure of pearls, with the 

 view of forcing the shell-fish to produce them. 

 When describing the turquoise-mines of the south 

 of France, and the means adopted to make the 

 mineral assume a blue colour, he discovered that 

 these alleged stones were the teeth of a large ani- 

 mal, which is now known under the name of the 

 mastodon. 



His most important labours, however, with refer- 

 ence to the arts, were his researches respecting iron 

 and steel, which he published in 1722, in a sepa- 

 rate work under the title of Traite sur I'art de con- 

 vertir le fer en acier, et d'adoucir le fer fondu. At 

 this period all the steel that was used in France was 

 imported, none having previously been made in that 

 country ; and one may imagine how numerous and 

 patient were the trials made by Reaumur before 

 he succeeded in his object. The Duke of Orleans 

 rewarded him for this valuable discovery, by be- 

 stowing on him a pension of 12,000 livres. In like 



