New Theories in Astronomy — Background and Themes

Challenging the Inverse-Square Law

Stirling’s first major target is the application of the inverse-square law to particles within a spherical shell. He asserts that the standard conclusion—that such a particle feels no net force—is false, and he provides a numerical example to demonstrate his point. The excerpt shows him working through calculations of volume and mass distribution, arguing that the outer half of the Earth’s volume contains only 70.5% of half the mass, while the inner half contains 29.5% more. He concludes that this disproves the homogeneity assumed by prevailing theories. His method is arithmetic rather than experimental, relying on geometric division of the sphere into concentric layers.

The Moon’s Rotation: A Gin Horse Analogy

In Chapter II, Stirling turns to the Moon, denying that it rotates on its axis. He uses an analogy of a gin horse—a horse walking in a circle to drive a mill—to argue that revolution does not imply rotation. He writes that a gin horse “does not rotate on its axis in its revolution,” and extends the analogy to the Moon, claiming that centrifugal force would be sufficient to drive air and water, but not to cause rotation. This section reveals his reliance on mechanical reasoning drawn from his engineering background, applying terrestrial analogies to celestial mechanics.

Earth’s Internal Structure: Hollow or Solid?

Stirling questions the solidity of the Earth’s interior, proposing instead a hollow structure. He calculates that if the Earth were divided into two equal volumes at a depth of 817 miles, the inner half would have nearly twice the mass of the outer half under his assumptions. He finds this implausible if the original cosmic matter was homogeneous, and sarcastically suggests that otherwise a “superintendent” must have placed heavier matter at the center. He then speculates on convection currents and heat conduction, arguing that a solid nucleus would prevent upward movement of matter. His reasoning is speculative but grounded in the physical principles of density and gravitation.

The Author’s Engineering Perspective

Stirling’s background as a civil engineer shapes his approach throughout the excerpts. He treats astronomical problems as mechanical ones, using analogies from machinery (gin horse) and construction (mounds of matter). His calculations are presented as straightforward arithmetic, often without reference to observational data. The “To the Reader” note reveals he died before publication, and the work was issued posthumously. Readers should note that Stirling’s arguments are not those of a professional astronomer but of an engineer applying practical reasoning to theoretical questions. This perspective gives the book a distinctive voice, but also means its claims should be evaluated with an understanding of the author’s limited access to contemporary astronomical evidence.

Stirling’s New Theories in Astronomy is best approached as a historical document of independent scientific thought rather than a textbook. Readers interested in the development of gravitational theory or in 19th-century amateur science will find his arguments revealing, especially his reliance on arithmetic and mechanical analogy. The book rewards careful reading of its numerical passages, where Stirling’s engineering mindset is most evident.

Stirling’s arithmetic made me think of my father’s old brass telescope, the one we’d set up on winter evenings. He never cared much for theory—just the quiet pleasure of finding Saturn’s rings. That same patient wonder filled Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. — A Closer Reading, where the sky felt less like a problem and more like a room we could visit.