W: Thornton returns his respectful Compliments to the President of the United States.—He has perused, and returns Mr: Elgar’s Letter; but is not acquainted with any Species of Serpentine Stone which he thinks can possibly possess the magnetic Power, as it is a species of Calcarious Stone, or Marble, denominated from its Spots and variegated appearance, not endued, to the best of his knowledge, with any peculiar quality. Indeed if any Stone exists subject to polar attraction, but not obedient to Iron, it might nevertheless be still subject to Loadstone, which no doubt abounds in various parts of our Country. The Inconveniences Mr: Elgar complains of are great, & the Correction would be of Consequence. The very Idea of a remedy may lead to Success.—