Give an account of astronomer came in the flying island of laputa

From the text:

At the centre of the island there is a chasm about fifty yards in diameter, whence the astronomers descend into a large dome, which is therefore called flandona gagnole, or the astronomer's cave, situated at the depth of a hundred yards beneath the upper surface of the adamant. In this cave are twenty lamps continually burning, which, from the reflection of the adamant, cast a strong light into every part. The place is stored with great variety of sextants, quadrants, telescopes, astrolabes, and other astronomical instruments.