In plain words
There is the hare. It breathes in and out forty or fifty times a minute. It can live only five or six years. As fast as the breath goes in and out, so fast does life come to its end. The more slowly these breaths go in and out, the longer we can live. How should this breath be let out? We must not let out the breath forcefully, thinking, “We have strength, after all.” If we hold flour in the hand and keep it near the nose, then as this breath lets out its air, not even the flour should stir. That is how gently it must be let out. To have the breath go in and out with such calm and slowness, the practice of yoga is of some use. To achieve this, all the ṛṣis of those days lived in the forest. They went to the forests to achieve things like purity of speech and control of the senses, and not with any other aim.
And the meditations they practised: what were they like? The first is dhāraṇā. Twelve dhāraṇās make one dhyāna, they said. Twelve dhyānas make one samādhi, they said. What is dhāraṇā? To look at one object for twelve seconds without wavering in any direction: that is dhāraṇā. Set before you some photo, some object, some image, set yourself some time, twelve seconds, and practise it well. For twelve seconds, letting it go nowhere, set your whole gaze on that object. Twelve seconds is not a long time. Doing dhāraṇā in this way makes room for dhyāna. For only twelve seconds we must hold our gaze on one object. This is dhāraṇā. After dhāraṇā comes dhyāna. When there have been twelve such dhāraṇās, it becomes one dhyāna. What does that mean? Twelve times twelve is a hundred and forty-four seconds. Two minutes and twenty-four seconds. Dhyāna is not sitting for hours on end. If it is true dhyāna, two minutes and twenty-four seconds are enough; only when we go on practising this dhāraṇā well is there a chance for the two minutes and twenty-four seconds called dhyāna to hold steady. Twelve dhyānas make one samādhi, they said. That is, a hundred and forty-four times twelve: twenty-eight minutes and forty-eight seconds. This is samādhi. It is not even an hour. Only this much is samādhi. Any longer, and it is the samādhi of the grave. It is departure. The breath of life does not come back again. This is the discipline they followed.
Neither the Śāstras nor any pandit has spoken of this discipline anywhere. To achieve this, we must first enter into dhāraṇā. Keep doing this dhāraṇā, for twelve seconds only. It is very necessary for the children. In the past, many ṛṣis, Aurobindo Ghose, Ramaṇa Maharṣi, all of them, carried on with this kind of practice. Leave Aurobindo aside; Ramaṇa Maharṣi used to go up onto the terrace at night.