Edmond Halley (1656-1742), in Philosophical Transactions of Royal Society raised the idea of a hollow Earth, with a solid sphere in the center. The publication was to explain the magnetic anomalies of the compass readings. Halley suggested that the atmosphere inside the earth was luminous (and possibly inhabited) and that the gas escaped was responsible for the Aurora Borealis.
For Halley, the Earth would be a shell of 500 miles thick, with three concentric spheres about the diameter of the planets Venus, Mars and Mercury. Halley assumed that the spaces between the spheres in his model, was representative of the atmospheres of them.
Assuming as unity the diameter of Earth, Mercury is 0.38 the diameter of Earth, Mars and Venus is 0.53 is 0.95. With these data we can assume that Halley thought that in the very center of the Earth was the lowest of the spheres, representing Mercury. Then you should follow the sphere of Mars, which in turn should also be hollow to accommodate the Mercury sphere. Finally, the sphere of Venus, very close to the planet's surface, but also hollow to accommodate the field of Mars (which itself was inside that of Mercury). Thus, for Halley, the Earth is not completely empty, but occupied by concentric hollow spheres, one inside the other areas [...] rotating at different speeds and oceans [...] filtered inwards" for the provisions that the Creator had taken".
A comparison between Kepler's harmony among planet orbits from the Sun outwards, and Halley's concentric spheres toward the center of the Earth.
If we recall the geometric model of Kepler, a century earlier, in which he adapted the spheres of the first five orbits of planets within the five Platonic solids, we realize that what Halley did was similar to Kepler's model (1571-1630). Obviously, the Keplerian arrangement was had some solid foundations that are based on actual calculations of planetary orbits. What Kepler did is still valid because the orbits today have the same diameters of yesteryear, but what Halley did is now only a historical curiosity.
However, there is a common denominator between these two dedicated and famous astronomers: in both cases they tried to find a justification for the existence of planets based on the harmony between the diameters of the planetary orbits. In both cases, the distances and diameters of the planets are not a product of long planetary evolution, but the planets are there because they were put there by the provisions that the Creator had made.
The arrangement of Kepler has a beauty that still one wonders why there is this amazing coincidence. In contrast, in Halley's model, the fact that the spheres corresponding to the planets are placed one inside each other, and the planet Mars is one of them, makes us question why the place Mars, although it is diameter smaller than Earth, its orbit is greater. This takes away the beauty and harmony of Kepler's model and makes us conclude that Halley's model is a model forced one.
The idea that the Earth is hollow is a long story before Halley made it popular. To review some data, Archelaus ca. 500 (before the Christian era) was talking about how the Earth was "a swamp ... hollow in the center" and by 1616, another person named Balthasar van der Veen had also another theory that incorporated the idea of the hollow Earth. Griffin, in his article: What Curiosity in the Structure: The Hollow Earth in Science expands the list and includes proponents, advocates or hollow Earth mentioning Plato, Aristotle, Lucretius, Seneca, and Dante.
''Earthquakes and volcanoes, the holes in the ground, springs and wells were sufficient to show that not everything is solid under our feet. The caverns and caves provide direct access to foreign inverted worlds beneath the surface of the Earth, while (in the absence of mechanistic understanding about how they form) fossils and other geological events reasonably suggest that they not only exist, but hosts strange creatures", says Griffin.
And then continues: "The need to reconcile the large number of geographical and geological information with the Mosaic accounts of creation and the Flood was the formulation of theories about the Earth a popular activity at the same time a moral necessity in the intellectual elite the seventeenth century, one that generated a scholarly debate and popular interest at the same time. Two books of that period - in particular stand out: the Mundus subterraneus by the Jesuit Athanaisius [Athanasius] Kircher, published in Amsterdam in 1664 and Sacred Theory of the Earth cleric Thomas Burnet, in 1681".
It was while gathering data for his research of weather and topographic that Halley met with two difficulties which he described: "not easy to solve". The first was that "there is no magnet that I have heard with more than two opposite poles, while the Earth obviously has four, and maybe more. The second difficulty was that the poles were not fixed on the Earth".
If Halley believed that the earth had more than two poles in his time was because the tabulated data of geomagnetic positions was very limited, incomplete and fragmented, "especially near the poles", says Griffin. So not surprisingly, Halley believed that the Earth had more than two poles. But what most contributed that Halley postulated a hollow Earth was Newton's error in the estimate of the relative densities of the Earth and Moon. "Newton's estimate of a dense Moon provided Halley the key to solving the dilemma with which he lived for eight years". For Halley, the Earth was not only hollow, but also had an inner sphere that floated under us.
After pointing out the possible arguments to his theory, Halley displays other arguments. He invokes the rings of Saturn as natural analogy and evidence that nested bodies may share a common center and held in place by gravity.
''In the days of Halley", Griffin continues, "the question of utility was a significant issue that could not be ignored". That is, he could ask what is the use of an sphere within our hollow Earth and was considered a reasonable question, to which Halley replied: "Why do we think that this prodigious mass of matter will only serve to maintain the surface? Why not best to assume that it has been mandated by the Supreme Wisdom that it can also serve as a surface for the use of living creatures ..."
All this was previously answered Bernard Bovier de Fontenelle, in his book The plurality of worlds where he argued that there must be life on every planet; it is impossible to imagine any other use. Halley, influenced by this thought must have thought that same as above should be like below: if there are spheres outside to sustain life, the ultimate function of an inner sphere should be the same. To the problem of light to these inner worlds "Halley professes humble ignorance noting that 'there are many ways that we do not know to produce light ..."
To Sir John Leslie is credited with saying that there are two suns, which gave them the names Pluto and Proserpina. Cotton Mather was influenced by these ideas and included them in his book, Christian Philosopher, and Leslie's ideas were the inspiration for Jules Verne's Journey to the Center of the Earth.
Jules Verne's Journey to the Center of the Earth is perhaps one of the best known and disseminated of his prolific career. Journey to the Center of the Earth was published in 1863, but more than a century before, in 1741, Ludvig Holberg, a Danish writer to which Humboldt refers, published a Latin work titled Nicolai Klimii iter subterraneum (Journey to the underworld Nicolai Klimii). Holberg's work seems to be closer in time to the ideas of Halley and Leslie.
However, the idea that Leslie suggested that in the center of the Earth there must be two suns, is widespread, but in an intensive search on what was actually proposed by him, or from a reliable source "resulted in that apparently he did not. Alexander von Humboldt, in his book Cosmos: A Sketch of the Physical Description of the Universe, Vol 1, says that Leslie "has cleverly designed the core of the earth full of imponderable matter which has an enormous force of expansion. These arbitrary and adventurous conjectures have led in circles completely unscientific, more fantastic notions. Hollow Earth has been slowly becoming alive with plants and animals, and two small subterranean spinning planets Pluto and Proserpina, were imaginatively supposed to shed light on his tenuous". That is, Leslie apparently, never proposed the Suns attributed to him.
Halley concluded that the Earth must be hollow by purely astronomical reasoning: his reasoning was based on comparison of relative densities of the Earth and Moon, but based on erroneous calculations of Newton who then corrected them, but Halley continued to maintain his idea of Hollow Earth.
On the other hand, Leslie also came to the conclusion that the Earth must be hollow, but by deductions other than those of Halley. Leslie was based on "the theory of compression of bodies" in which it was assumed that water is incompressible, but Leslie believed that the water he could be.
The common denominator in both theories, Halley's and Leslie's, is that both were based on false premises, but, curiously reached the same conclusion; an outcome even more surprising because it is believed that Leslie did not know the theory of Halley.
According to Griffin, the Suns at the center of the Earth are a must for Leslie because if the earth was hollow, space could be filled simply with air, because air is compressible because it would have ended in disaster. Instead of that substance, "the vast underground cavity should be filled with some highly diffusive, with an amazing elasticity or internal repulsion between molecules ... This leaves only one possibility: ... the only fluid known to possess this characteristic is the LIGHT itself".
This leads us ... the most important and impressive conclusion. The large central concavity is not that dark and depressing abyss that the fanciful poets had painted for us. On the contrary, this spacious internal vault should contain the purest essence of ethereal light in its most concentrated state, glowing with a strong and pervasive effulgence splendor.
Sir John Leslie.
This article is an excerpt from my work not yet published, titled: Universo Inconcluso: Las fechas y sucesos que moldearon en el ser humano la idea del universo. (Unfinished Universe: The dates and events that shaped in the human being the idea of the universe.) In this work all the bibliographic citations are documented, but in this version for the Internet, the text has been simplified.
The EBook: Journey to the Underground by Louis Holberg is available for free download in our EBook Catalog.