Page:Swedenborg, Harbinger of the New Age of the Christian Church.djvu/72

 his Algebra, a 16mo of 135 pages, was printed in 1718. Of works of this period in manuscript there are still preserved an essay on the Importance of Instituting an Astronomical Observatory in Sweden; one on the Causes of Things; a New Theory concerning the End of the Earth, in which he holds that the earth revolves in a resisting medium and is gradually retarding its motion and approaching the sun; a Project for Assisting Commerce and Manufactures, by controlling the export of Swedish iron and copper; a Memorial on the Establishment of Salt-works in Sweden; an Essay on the Nature of Fire and Colors; and some discussions of higher mathematics, involving the Differential and Integral Calculus. Of the direction of his studies at this time, the following letter to Benzelius, written 30th January, 17 18, gives further information:—

"I send you something new in physics, on the particles of air and water, proving them to be round, which may militate against the philosophy of many; but as I base my theory upon experience and geometry, I do not expect that any one can refute it by arguments. Preconceived ideas received from Descartes and others will be the