SOURCE: "Of the Copernican System" in An Account of the Astronomical Discoveries of Kepler, The University of Wisconsin Press, 1963, pp. 81-92.

In the following excerpt from an essay originally written in 1804, Small discusses how Copernicus came to his conclusions regarding heliocentrism and the diurnal rotation of the earth.

Though the imperfections of the Ptolemaic system were not immediately perceived, especially during the confusion which attended the decline and destruction of the Roman empire, their effects did not fail, in process of time, to become fully evident. In the ninth century, on the revival of science in the east, under the encouragement of the caliphs, surnamed Abassides, Ptolemy's astronomical tables were found to deviate so widely from the actual situations of the celestial bodies, as to be no longer useful in calculations: and it became necessary for the Saracen astronomers at Bagdat to form tables entirely new. The Saracens...