In the eighteenth century not only did they get their pearls from European rivers instead of from the East; but, instead of being excited about the artificial production of diamonds, they were driven wild with astonishment by the demonstration of the volatilisation of these stones--the disappearance of diamonds into invisible vapour when sufficiently heated. That the hardest stone in nature could be thus dissipated into thin air seemed incredible. On Aug. 10, 1771, a chemist named Rouelle invited to his laboratory to witness this wonder a company comprising the Margrave of Baden and the Princess his wife, the Dukes of Chaulne and of Nivernois, the Marchionesses of Nesle and of Pons, the Countess of Polignac, and some members of the Academy of Sciences, including the great chemist Lavoisier. Four diamonds--the largest belonging to the Count Lauraguais--were submitted before the eyes of all to the heat of a furnace, and in three hours had completely evaporated. There was, no doubt, room here for a mystification and for the abstraction of the diamonds with a view to dishonest appropriation. But no such purpose existed. The experiment was a genuine one, and Rouelle and his brother were honest investigators. They established the fact, now demonstrated as a lecture experiment, that the diamond is volatilised at very high temperatures. A more celebrated “evaporation” of diamonds--that which is known as “the affair of the Queen’s necklace”--took place a few years later in Paris, when no scientific investigation was connected with the embarrassing disappearance of the Royal trinket. 35. _A King Who was a Zoologist_ The King of Portugal, Carlos di Braganza, who was assassinated in the spring of 1908, was one of the most gifted and vigorous men of his age, fearless and intelligent to a rare degree, good-hearted, and devoted to the welfare of his people. If any man were justified in having no fear of outrage because he was conscious that his uprightness was proved and known to all men, his benevolence experienced by all, his ability and vast knowledge recognised by all, Dom Carlos was that man. Fanaticism, however, takes no account of the virtues of its victims. Until society has invented a method for keeping instruments of destruction out of the reach of dangerous, more or less maniacal individuals, all those who excite the fanatic’s brain, even by the excellence and nobility of their lives, risk death whenever they trust themselves to the tender mercies of a crowd. Psychology may one day enable us to detect, and improved supervision of children enable us to segregate before it is too late, the latent assassins in our midst. If they have not a king as their quarry their reason is palsied by a president, and were there no presidents, they would become homicidal in the presence of a prefect or a policeman--even of a professor.