24 NATURAL HISTORY OF PRECIOUS STONES, &c. by experiment. "Whilst admitting, and to the fullest extent, all their medicinal virtues * as set forth in the me­diaeval Lapidaria, giving recipes for the extracting the " Spirit of Emerald," for compounding the " Ointment of Lapis-lazuli," and exhibiting the " Powder of Coral," &c, he denounces the belief in their magical potency for a snare of the Devil, equally as superstitious as derogatory to the idea of Divine Providence. To give a notion of his philosophy on this head : " The effects of gems are generally material, in few cases spiritual, and then only when acting through some means that must be held the efficient cause rather than the gem itself. For example, if the Carnelian, Jasper, or Haematite, be worn by a person that has suf­fered from the discharge of blood, and is thereby rendered weak both in muid and body, and the discharge be so stopped, it is possible that by means of this retention of its blood the heart may be so much invigorated, and the temperament of the person so far restored, that the individual may acquire courage in the place of cowardice, which indeed is an immaterial quality, but nevertheless dependent upon something material, namely the blood ; as do every habit of the soul and act of the mind. But such effects as these, having a nearer cause, the abundance of the blood, cannot be properly ascribed to the gem itself. But that wisdom, eloquence, memory, and other virtues and habits of mind, can be generated or strengthened by the wearing of gems, as people have hitherto believed, is a great absurdity. For these qualities do not depend upon the humours and the spirits, as do cowardice, bashfulness, and timidity, but upon a part of the rational soul, and upon use productive of the habit."