In the astral body are all the centres of your senses. You know how after death a man's desires are the same as they were during his physical life. You know how in dreams your desires resemble desires that you may have in your waking consciousness. The centre of all your psychic powers, of your conscious powers, the centres of these are in the astral, and if (especially with your senses, each of which has its own centre in the astral body) you overstrain the physical senses down here, you will get an action on the astral plane, but an unhealthy, because disorderly one, one not going along the line of evolution but trying to create from below instead of from above. None the less, you may have some results, and in the two famous Indian systems for developing the powers of the consciousness, and for unfolding the consciousness itself, you have this recognised, and you read of Râja Yoga and of Hatha Yoga, of the Kingly Yoga and of the Yoga of Effort. The Yoga of Effort is Hatha Yoga, and is practised by physical means and followed by physical effects. The eye is stimulated in certain ways, and the effect of straining the physical eye is to bring about a certain limited kind of clairvoyance. You can gain it in that way by gazing into crystals, and so on. They do stimulate the centre of physical sight, but not the astral; and that is why they cannot go very far. You can get a certain amount of clairvoyance by these means, but you are only expanding your physical sight, and working on centres of the astral body connected with the physical organ of vision, the eye. The true astral sight is an entirely different thing. That comes from a centre of its own in the astral body. It has to be created from the mental body, as the organ of the physical was from the astral. The centre of that sight will be in the mental body and not in the astral, and only the organ of it in the astral body. The method of the Kingly, the Râja Yoga, is always by thought--concentrate, meditate, contemplate, think: by that means, in a healthy, normal, natural way you will inevitably develop the powers of sight on the astral, as in the course of Nature the powers of sight were developed on the physical plane. And if you realise that your consciousness is one, building its bodies for its fuller and more complete expression, that you are here in order to become masters of matter instead of its slaves, to become lords of matter, using every organ of matter for knowledge of the world to which that matter belongs, and not to be blinded by it, as we are for so long a time in our climb upwards, then you will see that this natural development of astral powers is inevitable in the course of evolution, and all that you can do is to quicken it, following the line which Nature has traced. As Nature slowly will evolve in every human being the power of using the astral body as freely as you use the physical body now, so can you quicken the coming of that day for