According to the Yogis, there are two nerve currents in the spinal column, called Pingalā and Idā, and a hollow canal called Sushumnā running through the spinal cord. At the lower end of the hollow canal is what the Yogis call the "Lotus of the Kundalini". They describe it as triangular in form in which, in the symbolical language of the Yogis, there is a power called the Kundalini, coiled up. When that Kundalini awakes, it tries to force a passage through this hollow canal, and as it rises step by step, as it were, layer after layer of the mind becomes open and all the different visions and wonderful powers come to the Yogi. When it reaches the brain, the Yogi is perfectly detached from the body and mind; the soul finds itself free. We know that the spinal cord is composed in a peculiar manner. If we take the figure eight horizontally („) there are two parts which are connected in the middle. Suppose you add eight after eight, piled one on top of the other, that will represent the spinal cord. The left is the Ida, the right Pingala, and that hollow canal which runs through the centre of the spinal cord is the Sushumna. Where the spinal cord ends in some of the lumbar vertebrae, a fine fibre issues downwards, and the canal runs up even within that fibre, only much finer. The canal is closed at the lower end, which is situated near what is called the sacral plexus, which, according to modern physiology, is triangular in form. The different plexuses that have their centres in the spinal canal can very well stand for the different "lotuses" of the Yogi.
The Yogi conceives of several centres, beginning with the Mulādhāra, the basic, and ending with the Sahasrāra, the thousand-petalled Lotus in the brain. So, if we take these different plexuses as representing these lotuses, the idea of the Yogi can be understood very easily in the language of modern physiology. We know there are two sorts of actions in these nerve currents, one afferent, the other efferent; one sensory and the other motor; one centripetal, and the other centrifugal. One carries the sensations to the brain, and the other from the brain to the outer body. These vibrations are all connected with the brain in the long run. Several other facts we have to remember, in order to clear the way for the explanation which is to come. This spinal cord, at the brain, ends in a sort of bulb, in the medulla, which is not attached to the brain, but floats in a fluid in the brain, so that if there be a blow on the head the force of that blow will be dissipated in the fluid, and will not hurt the bulb. This is an important fact to remember. Secondly, we have also to know that, of all the centres, we have particularly to remember three, the Muladhara (the basic), the Sahasrara (the thousand-petalled lotus of the brain) and the Manipura (the lotus of the navel).
Next we shall take one fact from physics. We all hear of electricity and various other forces connected with it. What electricity is no one knows, but so far as it is known, it is a sort of motion. There are various other motions in the universe; what is the difference between them and electricity? Suppose this table moves — that the molecules which compose this table are moving in different directions; if they are all made to move in the same direction, it will be through electricity. Electric motion makes the molecules of a body move in the same direction. If all the air molecules in a room are made to move in the same direction, it will make a gigantic battery of electricity of the room. Another point from physiology we must remember, that the centre which regulates the respiratory system, the breathing system, has a sort of controlling action over the system of nerve currents.
Now we shall see why breathing is practised. In the first place, from rhythmical breathing comes a tendency of all the molecules in the body to move in the same direction. When mind changes into will, the nerve currents change into a motion similar to electricity, because the nerves have been proved to show polarity under the action of electric currents. This shows that when the will is transformed into the nerve currents, it is changed into something like electricity. When all the motions of the body have become perfectly rhythmical, the body has, as it were, become a gigantic battery of will. This tremendous will is exactly what the Yogi wants. This is, therefore, a physiological explanation of the breathing exercise. It tends to bring a rhythmic action in the body, and helps us, through the respiratory centre, to control the other centres. The aim of Prānāyāma here is to rouse the coiled-up power in the Muladhara, called the Kundalini.
Everything that we see, or imagine, or dream, we have to perceive in space. This is the ordinary space, called the Mahākāsha, or elemental space. When a Yogi reads the thoughts of other men, or perceives supersensuous objects he sees them in another sort of space called the Chittākāsha, the mental space. When perception has become objectless, and the soul shines in its own nature, it is called the Chidākāsha, or knowledge space. When the Kundalini is aroused, and enters the canal of the Sushumna, all the perceptions are in the mental space. When it has reached that end of the canal which opens out into the brain, the objectless perception is in the knowledge space. Taking the analogy of electricity, we find that man can send a current only along a wire, (The reader should remember that this was spoken before the discovery of wireless telegraphy. — Ed.) but nature requires no wires to send her tremendous currents. This proves that the wire is not really necessary, but that only our inability to dispense with it compels us to use it.
Similarly, all the sensations and motions of the body are being sent into the brain, and sent out of it, through these wires of nerve fibres. The columns of sensory and motor fibres in the spinal cord are the Ida and Pingala of the Yogis. They are the main channels through which the afferent and efferent currents travel. But why should not the mind send news without any wire, or react without any wire? We see this is done in nature. The Yogi says, if you can do that, you have got rid of the bondage of matter. How to do it? If you can make the current pass through the Sushumna, the canal in the middle of the spinal column, you have solved the problem. The mind has made this network of the nervous system, and has to break it, so that no wires will be required to work through. Then alone will all knowledge come to us — no more bondage of body; that is why it is so important that we should get control of that Sushumna. If we can send the mental current through the hollow canal without any nerve fibres to act as wires, the Yogi says, the problem is solved, and he also says it can be done.
This Sushumna is in ordinary persons closed up at the lower extremity; no action comes through it. The Yogi proposes a practice by which it can be opened, and the nerve currents made to travel through. When a sensation is carried to a centre, the centre reacts. This reaction, in the case of automatic centres, is followed by motion; in the case of conscious centres it is followed first by perception, and secondly by motion. All perception is the reaction to action from outside. How, then, do perceptions in dreams arise? There is then no action from outside. The sensory motions, therefore, are coiled up somewhere. For instance, I see a city; the perception of that city is from the reaction to the sensations brought from outside objects comprising that city. That is to say, a certain motion in the brain molecules has been set up by the motion in the incarrying nerves, which again are set in motion by external objects in the city. Now, even after a long time I can remember the city. This memory is exactly the same phenomenon, only it is in a milder form. But whence is the action that sets up even the milder form of similar vibrations in the brain? Not certainly from the primary sensations. Therefore it must be that the sensations are coiled up somewhere, and they, by their acting, bring out the mild reaction which we call dream perception.
Now the centre where all these residual sensations are, as it were, stored up, is called the Muladhara, the root receptacle, and the coiled-up energy of action is Kundalini, "the coiled up". It is very probable that the residual motor energy is also stored up in the same centre, as, after deep study or meditation on external objects, the part of the body where the Muladhara centre is situated (probably the sacral plexus) gets heated. Now, if this coiled-up energy be roused and made active, and then consciously made to travel up the Sushumna canal, as it acts upon centre after centre, a tremendous reaction will set in. When a minute portion of energy travels along a nerve fibre and causes reaction from centres, the perception is either dream or imagination. But when by the power of long internal meditation the vast mass of energy stored up travels along the Sushumna, and strikes the centres, the reaction is tremendous, immensely superior to the reaction of dream or imagination, immensely more intense than the reaction of sense-perception. It is super-sensuous perception. And when it reaches the metropolis of all sensations, the brain, the whole brain, as it were, reacts, and the result is the full blaze of illumination, the perception of the Self. As this Kundalini force travels from centre to centre, layer after layer of the mind, as it were, opens up, and this universe is perceived by the Yogi in its fine, or causal form. Then alone the causes of this universe, both as sensation and reaction, are known as they are, and hence comes all knowledge. The causes being known, the knowledge of the effects is sure to follow.
Thus the rousing of the Kundalini is the one and only way to attaining Divine Wisdom, superconscious perception, realisation of the spirit. The rousing may come in various ways, through love for God, through the mercy of perfected sages, or through the power of the analytic will of the philosopher. Wherever there was any manifestation of what is ordinarily called supernatural power or wisdom, there a little current of Kundalini must have found its way into the Sushumna. Only, in the vast majority of such cases, people had ignorantly stumbled on some practice which set free a minute portion of the coiled-up Kundalini. All worship, consciously or unconsciously, leads to this end. The man who thinks that he is receiving response to his prayers does not know that the fulfilment comes from his own nature, that he has succeeded by the mental attitude of prayer in waking up a bit of this infinite power which is coiled up within himself. What, thus, men ignorantly worship under various names, through fear and tribulation, the Yogi declares to the world to be the real power coiled up in every being, the mother of eternal happiness, if we but know how to approach her. And Rāja-Yoga is the science of religion, the rationale of all worship, all prayers, forms, ceremonies, and miracles.