Chandogya Upanishad is one of the oldest Upanishad written on the Vedic Brahmana period about ninth to eighth century BC. Chandogya Upanishad is associated with Sama Veda. It is ranked ninth in the Muktika canon of hundred and eight Upanishadas. The 18th khanda of Chandogya Upanishad deals with the mind and the akasa as symbols of Brahman. According to it one must meditate on the mind as Brahman. This is in association with the body. One must also adorn and meditate on the akasa as Brahman. This is said with reference to the gods. These are the two intellectual and theological forms of worship that have been ordained by sages. This Brahman has four feet or four quarters. Here speech is one foot, the prana i.e. the nose is one foot, the eye is one foot and the ear is one foot. This has been said with reference to body. Further it has been explained with reference to the gods. Here,
Agni i.e. fire is one foot, Vayu i.e. air is one foot, Aditya i.e. the sun) is one foot and the quarters i.e. disah are one foot. These are the two intellectual and theological forms of worship that have been ordained with reference to the body and with reference to the gods. The speech is essentially the fourth foot or quarter of Brahman. The mind is its symbol. It radiates light and heat through the effulgence of Agni. One who is aware of this and realises it shines and warms with fame, and shines with the radiance of Brahman. Prana i.e. the nose is fourth foot of Brahman. It radiates light and heat through the effulgence of Vayu or air. Heat and light radiate from his works. One who is aware of this and realises it shines and radiates with fame with the light of the Brahman. Again, the eye is a fourth foot of Brahman. It warms and radiates with the light of the Sun. It radiates light and heat through the effulgence of Aditya. One who is aware of this shines with fame with the light of Brahman. The ear is also the fourth foot of Brahman. It shines and radiates with the light of the quarters. One who is aware of this shines and warms verily.
