At the close of the seventeenth century, there was a famous impostor in France, whom the royal family, on account of his marvellous powers, invited to Paris. His name was James Aymar. I shall speak of him more fully hereafter; and refer to him, at present, in connection with a remark of Leibnitz. Aymar's imposture had no relation to the healing art, but the remark of Leibnitz is not, on that account, the less applicable. That great man wrote a letter, in 1694, which may be found in the Journal of Tenzelius, in which he refers to Aymar's fraud, and to his subsequent confession, before the Prince of Condè. Aymar said, according to Leibnitz, that he was led on, _non tam propria audacia, quam aliena credulitate hominum, falli volentium, et velut obtrudentium sibi_--not so much by his own audacity, as by the credulity of others, who were not only willing to be cheated, but actually thrust themselves upon him. All Paris was occupied, in attempting to explain the mystery of Aymar's performances, with his wonderful wand: and Leibnitz says-- _Nuper scripsi Parisios, utilius et examine dignius, mihi videri problema morale vel logicum, quomodo tot viri insignes Lugduni in fraudem ducti fuerint, quam illud pseudo-physicum, quomodo virga coryllacea tot miracula operetur_--I wrote lately to the Parisians, that a solution of the moral or logical problem, how it happened, that so many distinguished persons, in Lyons, came to be taken in, seemed to me of much greater utility, and far more worthy of investigation, than how this fellow performed miracles, with his hazel wand. It is worth noting, perhaps, that Leibnitz himself, according to the statement of the Abbé Conti, in the _Gazzette Litteraire_, for 1765, fell a victim to a quack medicine, given him by a Jesuit, for the gout. Ignorance is the hotbed of credulity. This axiom is not the less respectable, because the greatest philosophers, occasionally, place confidence in the veriest fools, and do their bidding. Wise and learned men, beyond the pale of their professional pursuits, or peculiar studies, are, very frequently, the simplest of simple folk--_non omnia possumus omnes_. Ignorance must be very common; for a vast majority of the human race have not proceeded so far, in the great volume of wisdom and knowledge, as that profitable but humiliating chapter, whose perusal is likely to stimulate their energies, by convincing them, that they are of yesterday and know nothing. Credulity must therefore be very common. Credulity has very little scope, for its fantastical operations among the exact sciences. Who does not foresee the fate of a geometrical quack, who should maintain, that the square of the hypothenuse, in a right-angled triangle, is either greater or less than the sum of the squares of the sides; or of the quack arithmetician, who would persuade our housewives, that of two and two pounds of Muscovado sugar, he had actually discovered the art of making five?