Resposta curta:
O Palantír de Elostirion foi projetado para olhar apenas para o oeste em direção à Pedra-Mestre na Torre de Avallonë e não se comunicar com os outros Palantíri na Terra-média. Provavelmente foi removido da Terra-média para impedir qualquer possível 'comunicação' ou 'visão' do Ocidente por aqueles deixados na Terra-média.
Long answer:
The Palantír of Elostirion, also known as the Elendil Stone was one of the Palantíri brought by the Faithful from Númenor. It was stored in the tower Elostirion on the Emyn Beraid by Elendil, and in later years was guarded by Círdan and the Elves of Lindon.[source?]
The stone was aligned westwards towards the Master-stone in the Tower of Avallonë, along the length of the Straight Road; because of this, it could not communicate with the other six of Middle-earth. Only Elendil was able to use it to look west across the Sea and see the Undying Lands;[1] Elendil also tried to see the fallen Númenor with the stone but failed.
Even after the fall of Arnor, Wandering Companies of Elves made pilgrimages to visit the Towers and see the Stone, in order to catch a glimpse of Varda. One such company, led by Gildor Inglorion just returning from Elostirion, was encountered by Frodo, Sam and Pippin on September 24, T.A. 3018.[2]
It remained in its tower until the end of the Third Age; it was then taken back into the West aboard the White Ship.[3]
Referências 1. ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), O Silmarillion, "Dos Anéis do Poder e da Terceira Era" 2. ↑ J.R.R. Tolkien, O Senhor dos Anéis, A Sociedade do Anel, "Três é Companhia" 3. ↑ J.R.R. Tolkien, O Senhor dos Anéis, O Retorno do Rei, "Os Portos Cinzentos"
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Elostirion was the tallest and westernmost of the three White Towers that stood on the Tower Hills[1] and that had been built by Gil-galad for Elendil. It held one of the palantír of Arnor which did not communicate with the rest but looked only westward across the Sundering Seas to Tol Eressëa. This, the last palantír of Arnor, was carried back across the sea with the departure of the ring-bearers early in the Fourth Age.[2]
Referências 1. ↑ J.R.R. Tolkien, O Senhor dos Anéis, "Prólogo", "Sobre Hobbits" 2. ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Contos Inacabados, "O Palantíri" link
Note: This is the best explanation I could find and will accept it unless someone can better explain.