Chandogya Upanishad 1.13.1

So long the Upaniṣad has shown how Sāma can be worshipped through the udgītha. Now another way of worshipping Sāma is being shown—through stobhas. Stobhas are syllables such as hiṃ, hāu, hāi, and so forth, and they are all from the Sāma Veda. By themselves these syllables have no meaning. They are symbols representing objects, or they are used to fill in gaps in sentences. The idea here is that stobhas like hāu should be applied to the earth, fire, etc.

A symbol has to have something in common with the object it represents. The Sāma Veda says, ‘This earth is also called rathantara.’ And in the Sāma, the stobha hāu stands for rathantara. Thus, it is reasonable to say that hāu stands for the earth.

The stobha hāi occurs in the Sāma called Vāmadevya. The Vāmadevya Sāma is about the relationship of air with water. This is why vāyu (air) is represented by the symbol hāi. Why is the moon represented by atha? This world is sustained by food (anna), and the moon and food are identical. A stands for anna, and tha stands for stha in sthita, which means ‘sustained.’ A plus tha is atha. Thus, atha can rightly be said to represent the moon.

Then the self is said to be iha, which means ‘here’ or ‘this,’ for the self is obvious to everyone. And the stobha ī represents fire, because wherever fire is referred to in the Sāma, the words end with ī.

The syllable ī then is rightly used as a symbol of fire, and to meditate on this symbol is to meditate on fire.