The Upanishads, Part 1 (SBE01), by Max Müller, , at sacred-texts.com
1. Let a man meditate on the fivefold Sâman 3 as the five worlds. The hiṅkâra is, the earth, the prastâva the fire, the udgîtha the sky, the pratihâra the sun, the nidhana heaven; so in an ascending line.
2. In a descending line, the hiṅkâra is heaven,
the prastâva the sun, the udgîtha the sky, the pratihâra the fire, the nidhana the earth.
3. The worlds in an ascending and in a descending line belong to him who knowing this meditates on the fivefold Sâman as the worlds 1.
23:3 The five forms in which the Sâman is used for sacrificial purposes. The Sâman is always to be under-stood as the Good, as Dharma, and as Brahman.
24:1 The commentator supplies some fanciful reasons why each of the five Sâmans is identified with certain objects. Earth is said to be the hiṅkâra, because both always come first. Agni is prastâva, because sacrifices are praised in the fire (prastûyante). The sky is udgîtha, because it is also called gagana, and both words have the letter g in common. The sun is pratihâra, because everybody wishes the sun to come towards him (prati). Heaven is nidhana, because those who depart from here are placed there (nidhîyante), &c.