In his inquiries into the business of ropemaking, for example, he proved by conclusive experiments that, contrary to the common opinion, twisting impairs the strength of ropes. Again, while describing the labours of the goldbeater, he took occasion to show the prodigious ductility possessed by certain substances. But, more especially, when examining the processes by which artificial pearls are coloured, he discovered the singular matter which gives lustre to the scales of fishes, and even explained the formation and growth of those scales. The colouring principle in glass pearls is obtained from the bleak (_Cyprinus alburnus_), an inhabitant of fresh water, and about six inches in length. This silvery ingredient is procured by macerating its scales in water, and is then mixed with a little isinglass. The small globes which are to represent pearls are first furnished with an internal coating of the solution, and then filled with melted wax to give them suitable weight. The pearly matter 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 animal, which is now known under the name of the mastodon.