It speaks not a little for the beauty of the emerald that so good a judge of precious stones as Pliny should have pronounced this gem to be the only one that delighted the eye without fatiguing it, adding that when the vision was wearied by gazing intently at other objects, it gained renewed strength by viewing an emerald. So general in the early centuries of our era was the persuasion that the pure green hue of emeralds aided the eyesight, that gem engravers are said to have kept some of them on their work-tables, so as to be able to look at the stones from time to time and thus relieve the eye-strain caused by close application to their delicate task.[484] Psellus says that a cataplasm made of emeralds was of help to those suffering from leprosy; he adds that if pulverized and taken in water they would check hemorrhages.[485] They were especially commended for use as amulets to be hung on the necks of children, as they were believed to ward off and prevent epilepsy. If, however, the violence of the disease was such that it could not be overcome by the stone, the latter would break.[486] Hermes Trismegistus says the emerald cures ophthalmia and hemorrhages. The great Hermes must have had a special preference for this stone, since his treatise on chemistry (_peri chemeias_) is said to have been found inscribed on an emerald.[487] By the Hindu physicians of the thirteenth century the emerald was considered to be a good laxative. It cured dysentery, diminished the secretion of bile, and stimulated the appetite. In short, it promoted bodily health and destroyed demoniacal influences. In the curious phrase of the school the emerald was “cold and sweet.”[488] Teifashi (1242 A.D.) believed that the emerald was a cure for hæmoptysis and for dysentery if it were worn over the liver of the person affected; to cure gastric troubles, the stone was to be laid upon the stomach. Furthermore, the wearer was protected from the attacks of venomous creatures, and evil spirits were driven from the place where emeralds were kept.[489] The direction to place the stone on the affected part, a recommendation often met with in the treatises on the therapeutic use of ornamental stones, shows that these were believed to send forth emanations of subtle power. Probably enough, the brilliant play of reflected light which proceeds from many of these gems suggested the idea that they radiated a certain curative energy. This theory need not surprise us, for, although it is altogether fanciful in the case of the diamond, ruby, emerald, etc., the newly discovered substance, radium, really possesses the active properties ascribed by old writers to precious stones. Jade