Category Archives: Books

Of Astronomy

When Jeremiah Mobley (1744-1826, Edgefield, S. C.) and his family read his copy of the Self-Instructor, they might have been led to believe that there was life on Mars and other planets. In the section on Astronomy, the “most sublime of all the sciences,” they would have read that Mars “has a considerable, but moderate atmosphere, so that its inhabitants probably enjoy a situation, in many respects, similar to ours.”

The sun was described as a “large and lucid planet,” solid, with an atmosphere and with mountains and valleys on its surface. Therefore, it was deducted that “it is most probably inhabited, like the rest of the planets, by beings whose organs are adapted to the peculiar circumstances of that vaster globe.” The Instructor explained how, by logic, the sun must have areas, like mountain tops, which would have cooler temperatures that would not “scorch up” everything on them. His knowledge of the approximate diameter of the sun and its size relative to the Earth’s size were pretty accurate, even though he underestimated its heat.

Astronomy was defined as the science concerning the motions of planets and stars. The Instructor explained how observation and logic determined that the earth was a sphere, and how scholars had debated whether the earth or the sun was the center of the universe.

The Mobleys may have consulted the book when they experienced the Great Comet of 1811, which presumably they and the rest of the world could see in the sky for the better part of a year, without a telescope. The Self-Instructor told them that comets remain in the sky for hundreds of years, and after fading out of sight, they will reappear to future generations. The Astronomy chapter also covered the topics of tides, eclipses, and stars, describing constellations and the Milky Way.

Astrology, however, was called a “malady of weak minds,” as the stars were considered to be too far away to influence human lives. Also, to know the future would destroy human confidence and motivation. Furthermore, the Instructor asserted that only “the light of science…can free us from the gross impositions of these wretched empiricks.” (An empiric being someone who believes in only what they can observe for themselves, as opposed, perhaps, to someone who believes, based on theory, that people live on the sun.)

On the other hand, farming according to the sun signs was a useful thing, as was telling time and navigating by the stars. Also important was the spiritual value of contemplating the vastness of the universe, enhanced by the elegant planetarium illustrated.

Sources: E. MacKenzie, The Self-Instructor; or Young Man’s Best Companion: Being a New, Sure, and Easy Guide to Knowledge, Virtue, and Happiness (Newcastle Upon Tyne: MacKenzie and Dent, 1827) pp. 263-290; “Great Comet of 1811,” Wikipedia,, accessed 9 Feb. 2018, last edited on 6 February 2018.

Copyright 2018 by Glenda Alexander.  All rights reserved.