Many of the hollow agates of southwestern Brazil and Uruguay contain a crop of amethyst crystals in the interior.

The Hollow Earth hypothesis proposes that the planet Earth is either entirely hollow or otherwise contains a substantial interior space.

Leslie did propose a hollow Earth in his 1829 Elements of Natural Philosophy ( pp. 449 – 453 ), but does not mention interior suns.

He supported the idea of a hollow Earth, but without interior shells or inner sun.

He placed an interior sun in the hollow Earth.

In the same time Vladimir Obruchev wrote a fiction novel Plutonia, where the hollow Earth's interior possessed one inner ( central ) sun and was inhabited by prehistoric species.

Instead of saying that humans live on the outside surface of a hollow planet, sometimes called a " convex " hollow-Earth hypothesis, some have claimed that our universe itself lies in the interior of a hollow world, calling this a " concave " hollow-Earth hypothesis.

Mystara is a hollow planet, with a habitable surface on its interior called the Hollow World.

The endosperm is initially in the nuclear phase of development within a hollow interior space as coconut water and air ( distinct from coconut milk ).

Visitors can take the " Tower Tour " where the interior of the hollow spire, with its ancient wood scaffolding, can be viewed.

In a rimfire case, centrifugal force pushes a liquid priming compound into the internal recess of the folded rim as the manufacturer spins the case at a high rate and heats the spinning case to dry the priming compound mixture in place within the hollow cavity formed within the rim fold at the perimeter of the case interior.

The hollow interior is called the neural canal.

Yellow marrow is found in the medullary cavity, the hollow interior of the middle portion of long bones.

Endoscopy means looking inside and typically refers to looking inside the body for medical reasons using an endoscope, an instrument used to examine the interior of a hollow organ or cavity of the body.

In the 18th century, for example, King Bodawpaya attempted to build the Mingun Pagoda, in the form of spacious vaulted chambered temple but failed as craftsmen and masons of the later era had lost the knowledge of vaulting and keystone arching to reproduce the spacious interior space of the Bagan hollow temples.

* In the first type of generator ( MK-1, 1951 ) developed by Robert Lyudaev, the magnetic flux produced by a wound conductor is confined to the interior of a hollow metallic tube surrounded by explosives, and submitted to a violent compression when the explosives are fired ; a device of the same type was developed in the USA a dozen years later by C. M.

The interior of Trajan's Column is hollow: entered by a small doorway at one side of the base, a spiral stair of 185 steps gives access to the platform above, having offered the visitor in antiquity a view over the surrounding Trajan's forum ; 43 window slits illuminate the ascent.

It rotates around its hub inside a gigantic hollow sphere with tiny " stars " affixed to the interior, complete with a small sun, moon and fake planets revolving around it.

The hollow interior also contains a small amount of DT gas.

There is an old and very large hollow river red gum ( Eucalyptus camaldulensis ), known as the Monarch of the Glen, that survives today in the centre of the caravan park ; its interior was partly burnt by adventurous Scouts many years ago, and it is now surrounded by a fence.

Such hollow coins were created from two ordinary coins, by milling out one face and the interior of both coins ( to create a cavity ), and the edges of one ( so it could slide into the other ).

* In biology, pertaining to the lumen, the interior of a hollow structure

The statue is hollow, and visitors can view the interior.

In the novel, his last contact with Earth is the radio message " The thing's hollow — it goes on forever — and — oh my God — it's full of stars!

The concept of a hollow Earth still recurs in folklore and as the premise for subterranean fiction, a subgenre of adventure fiction.

Edmond Halley in 1692 put forth the idea of Earth consisting of a hollow shell about thick, two inner concentric shells and an innermost core, about the diameters of the planets Venus, Mars, and Mercury.

In 1818, John Cleves Symmes, Jr. suggested that the Earth consisted of a hollow shell about thick, with openings about across at both poles with 4 inner shells each open at the poles.

An early twentieth-century proponent of hollow Earth, William Reed, wrote Phantom of the Poles in 1906.

He even built a working model of the hollow Earth and patented it ().

Other writers of the 20th century have proposed that " ascended masters " of esoteric wisdom inhabit subterranean caverns or a hollow Earth.

The writer David Hatcher Childress authored Lost Continents and the Hollow Earth ( 1998 ) in which he reprinted the stories of Palmer and defended the hollow earth idea based on alleged tunnel systems beneath South America and central Asia.

Fantastic stories ( supposedly believed as factual within fringe circles ) have also circulated that Adolf Hitler and some of his followers escaped to hollow lands within the Earth after World War II via an entrance in Antarctica.

Some writers have proposed building megastructures that have some similarities to a hollow Earth – see Dyson sphere, Globus Cassus.

In 2011, Horatio Valens and Paul Veneti presented a two-hour " Lazeria Map Collection " video on centuries-old maps of the Arctic region and the North Pole, making a case for a 100-mile wide canyon in the center of the physical North Pole, into which north-flowing rivers drain into a hollow Earth.

An example of a concave hollow Earth.

Purportedly verifiable hypotheses of a " concave hollow Earth " need to be distinguished from a thought experiment

Cyrus Teed, a doctor from upstate New York, proposed such a concave hollow Earth in 1869, calling his scheme " Cellular Cosmogony ".

Several twentieth-century German writers, including Peter Bender, Johannes Lang, Karl Neupert, and Fritz Braun, published works advocating the hollow Earth hypothesis, or Hohlweltlehre.

In one chapter of his book On the Wild Side ( 1992 ), Martin Gardner discusses the hollow Earth model articulated by Abdelkader.

Gardner rejects the concave hollow Earth hypothesis on the basis of Occam's Razor.

Another set of scientific arguments against a hollow Earth or any hollow planet comes from gravity.

Someone on the inside of a hollow Earth would not experience a significant outward pull and could not easily stand on the inner surface ; rather, the theory of gravity implies that a person on the inside would be nearly weightless.