Bringing them under the control of the will is what is called Pratyahara or gathering towards oneself. Fixing the mind on the lotus of the heart, or on the centre of the head, is what is called Dharana. Limited to one spot, making that spot the base, a particular kind of mental waves rises; these are not swallowed up by other kinds of waves, but by degrees become prominent, while all the others recede and finally disappear. Next the multiplicity of these waves gives place to unity and one wave only is left in the mind. This is Dhyana, meditation. When no basis is necessary, when the whole of the mind has become one wave, one-formedness, it is called Samadhi. Bereft of all help from places and centres, only the meaning of the thought is present. If the mind can be fixed on the centre for twelve seconds it will be a Dharana, twelve such Dharanas will be a Dhyana, and twelve such Dhyanas will be a Samadhi.