地球空洞説を主張していないLeonhard Euler

Leonhard Euler(1707-1783)は、Halleyの地球空洞説による磁極の説明を否定していたが、世の中的には支持者とされることがある。それは、おそらく地球空洞説を掲げたSymmes (1780-1829)か、その擁護者James McBrideによる創作と思われる。
The earliest mention of Euler in connection with the appears in James McBride's Symmes's Theory of Concentric Spheres (1826), the first extended and (fairly) coherent explication of Symmes' ideas. Symmes himself never did manage to produce a single document elaborating and putting them in order. Instead he wrote many short shotgun blasts about aspects of his theory that appeared as scattered newspaper articles, and he presented them in a series of ill-advised lectures from 1820 until his death in 1829. So the McBride book is the definitive source regarding his thinking.

After citing Halley's theory, McBride says that Euler was also an advocate but differed "as to the nature of the nucleus." He continues: "Euler believed it to be a luminous body formed of materials similar to the sun, and adapted to the purpose of illuminating and warming the interior surface of the crust, which he supposed might be inhabited equally with the exterior surface."

オイラーに関する最初の言及は、James McBrideの「Symmesの同心球の理論」(1826)にある。これは、Symmesのアイデアの最初の拡張された(かなり)一貫した説明である。Symmes自身はそれらの説明を整理して、ひとつの文書にまとめようとしたことはない。Symmesは代わりに、ばらばらの新聞記事に理論の一面を書き、それを1820年から死亡した1829年まで、一連の悪賢い講義でそれらを発表した。だから、McBrideの本が、Symmesの思考に関する決定的な情報源となっている。

Indeed, in Letters to a Princess of Germany, his widely read popularization of current science that appeared in three volumes between 1768 and 1772, Euler is categorically opposed to Halley's ideas about the earth's magnetism and the moving interior spheres that he suggests to account for it.


[ David Standish: "Hollow Earth: The Long and Curious History of Imagining Strange Lands, Fantastical Creatures, Advanced Civilization", Hachette UK, Sep 10, 2007, pp.42-43 ]

Euler was also an advocate for the theory of Dr. Halley. He believed, with him, that the earth is hollow, with a ball, or nucleus, included in the centre; he, however, differed from Halley as to the nature of the nucleus. Halley believed it to be constituted of the sum materials of the exterior crust of the earth. Euler believed it to be a luminous body formed of materials similar to the sun, and adapted to the purpose of illuminating and warming the interior surface of the crust, which he supposed might he inhabited equally with the exterior surface. He fancied that this luminous ball had no rotary motion, and that the outer shell revolved around it. However, neither he nor Dr. Halley left any opening by which the internal regions could be explored; their existence was therefore left to rest on vague hypo-thesis.


[ Symmes's Theory of Concentric Spheres: demonstrating that the Earth is hollow, habitable within, and widely open about the Poles. By a Citizen of the United States (i.e. James McBride), 1826, pp.132-133 ]


Euler's supposed proposition of a Hollow Earth is widely recounted but is probably apocryphal. When he wrote his Letters to a Princess of Germany, probably his most popular and widely read work, between 1760 to 1762, he clearly indicates his understanding that Earth is solid throughout. In Letter XLIX, concerning the "True Direction and Action of Gravity relatively [sic] to the Earth," he introduces a thought experiment, stating "were you to dig a hole in the earth, at whatever place, and continue your labor incessantly [...] you would, at length, reach the center of the earth" (Vol. 1, 219). Moreover, in Letters LVI- LIX, concerning magnetic declination, he discusses Halley's proposal at length. Concerning Halley's "double loadstone in the bowels of the earth" and four magnetic poles, he states: "this hypothesis seems to me rather a bold con-jecture" (Vol. 2, 253).


[ Hanjo Berressem, Michael Bucher, Uwe Schwagmeier: "Between Science and Fiction: The Hollow Earth as Concept and Conceit", LIT Verlag Münster, 2012, p.15 ]

"Letters to a Princess of Germany"のオリジナルと英訳を見てみると...
En effet fi l'on creufoit un trou dans la terre, en quelque lieu que ce foit , & qu'on continua't fans ceffe ce travail en creufant toujours en bas, on parviendroit enfin au centre de la terre.

In fact, were you to dig a hole in the earth, at whatever place and to continnue your labour incessantly, digging always downward and downward perpendicularly, you would at length reach the center of the earth.


[ Leonhard Euler: "Letter XLIX True Direction and Action of Gravity relatively to the Earth", 1768 (translated by David Brewster, 1823) (original) ]


Dans ce cas, les deux lignes sous lesquelles la déclinaison est nulle seraient des méridiens tirés par les pôles magnétiques. Donc, puisque nous avons vu qu'actuellement ces deux lignes, où il n'y a point de déclinaison, ne sont point des méridiens, mais qu'elles ont un tour bien bizarre, on voit bien que ce cas n'a point lieu sur la terre. Halley a bien reconnu cette conséquence, et s'est cru obligé par là de supposer un double aimant dans les entrailles de la terre, dont l'un serait fixe et l'autre mobile ; en conséquence, il a établi quatre pôles sur la terre , dont deux se trouvent près du pôle boréal, et les deux autres près du pôle méridional, à inégales distances. Mais cette conclusion me parait un peu hasardée : de ce que les lignes sans déclinaison ne sont point des méridiens, il ne- s'ensuit pas qu'il y ait quatre pôles magnétiques sur la terre; mois plutôt qu T il n'y en ait que deux, et que ces deux pôles ne soient pas directement opposés l'un à l'autre, ou, ce qui rouent au même, que l'axe magnétique ne passe point par le centre de la terre.

In this case, the two lines, under which there is no declination, would be the meridians drawn through the magnetic poles. But as we have seen that, in reality, these two lines without declination are not meridians, but take a very unaccountable direction, it is evident that no such case actually takes place. Halley clearly faw this difficulty, and therefore thought himself obliged to suppose a double load-stone in the bowels of the earth, the one fixed, the other moveable ; of consequence, he was obliged to admit four poles of the earth, two of them toward the north, and two toward the south, at unequal distances. But this hypothesis seems to me rather a bold conjecture: it by no means follows, that because these lines of no declination are not meridians, there must be four magnetic poles on the earth : but rather, that there are only two, which are not directly opposite to each other; or, which comes to the same thing, that the magnetic axis does not pass through the center of the earth.


[ Leonhard Euler: "Letter LIX, 1768 (translated by David Brewster, 1823) (XLII, original) ]

Edmond Halleyバージョンの地球空洞説における、4つの磁極を否定している。

Eulerの地球空洞説支持というネタは、Symmesの支持者の一人であるJames McBrideあるいはSymmesの創作のようである。