The Upanishads, Part 2 (SBE15), by Max Müller, , at sacred-texts.com
1. Bhû, Bhuvas, Suvas 4, these are the three sacred interjections (vyâhriti). Mâhâkamasya taught a fourth, viz. Mahas, which is Brahman, which is the Self. The others (devatâs) are its members.
Bhû is this world, Bhuvas is the sky, Suvas is the other world.
2. Mahas is the sun. All the worlds are increased by the sun. Bhû is Agni (fire), Bhuvas is Vâyu (air), Suvas is Âditya (sun). Mahas is the moon. All the heavenly lights are increased by the moon.
Bhû is the Rik-verses, Bhuvas is the Sâman-verses, Suvas is the Yagus-verses.
3. Mahas is Brahman. All the Vedas are increased by the Brahman.
(1-2) Bhû is Prâna (up-breathing), Bhuvas is Apâna, (down-breathing), Suvas is Vyâna (back-breathing). Mahas is food. All breathings are increased by food.
Thus there are these four times four, the four and four sacred interjections. He who knows these,
(1-2) Knows the Brahman. All Devas bring offerings to him.
48:1 The construction is not right. Woolly, lomasâ, is explained as 'possessed of woolly sheep.'
48:2 With the interjection Svâhâ each oblation is offered.
48:3 Bhaga, here explained as bhagavat.
48:4 The text varies between Bhû, Bhuvas, Suvas, Mahas, and Bhû, Bhuvar, Suvar, Mahar.