Valentine Greatrakes did unconsciously what many years after him Mesmer did by design. He in his remarkable career illustrated the power which a determined man may exercise over the will and nervous life of another. As soon as the singular properties of the loadstone were discovered, they were presumed to have a strong medicinal effect; and in this belief physicians for centuries--and indeed almost down to present times--were in the habit of administering pulverized magnet in salves, plaisters, pills, and potions. It was not till the year 1660 that it was for the first time distinctly recorded in the archives of science, by Dr. Gilbert, of Colchester, that in a state of pulverization the loadstone no longer possessed any magnetic powers. But it was not till some generations after this that medical practitioners universally recognized the fact that powder of magnet, externally or internally administered, was capable of producing no other results than the presence of any ordinary ferruginous substance would account for. But long after this error had been driven from the domains of science, an unreasonable belief in the power of magnets applied externally to the body held its ground. In 1779-80, the Royal Society of Medicine in Paris made numerous experiments with a view to arrive at a just appreciation of the influence of magnets on the human system, and came to the conclusion that they were medicinal agents of no ordinary efficacy. Such was the state of medical opinion at the close of the last century, when Perkins's tractors, which were supposed to act magnetically, became the fashion. Mr. Perkins was a citizen of Connecticut, and certainly his celebrated invention was worthy of the 'cutest people on the 'varsal earth. Barnum's swindles were modest ventures by comparison. The entire world, old and new, went tractor-mad. Every valetudinarian bought the painted nails, composed of an alloy of various metals (which none but Perkins could make, and none but Perkins sell), and tickled with their sharp ends those parts of his frame which were regarded as centres of disease.