The scientific, rational way to develop the astral senses is to first acquire the art of concentrating. Bear in mind that in concentration the person, while shutting out the impressions of the outside world in general, nevertheless focuses and concentrates his attention upon the one matter before him. This is quite a different thing from making oneself sensitive to every current of thought and feeling that may be in the psychic atmosphere. True concentration renders one positive, while the other methods render one negative. Contrary to the common opinion, psychic concentration is a positive state, not a negative--an active state, not a passive one. The person who is able to concentrate strongly is a master, while one who opens himself to "control," either physical or astral, is more or less of a slave to other minds. The student who will begin by experimenting along the lines of contact mind-reading, and who then advances along the lines of true telepathy, as explained in the earlier chapters of this book, will have made a good start, and considerable progress, along the road to clairvoyant development. The rest will be largely a matter of exercise and practice. He will be aided by practicing concentration along the general lines of the best occult teaching. Such practice may consist of concentration upon almost any physical object, keeping the thing well before the mind and attention. Do not tire the attention by practicing too long at one time. The following general rules will help you in developing concentration: (1) The attention attaches more readily to interesting rather than uninteresting things. Therefore, select some interesting thing to study and analyze by concentrated thought. (2) The attention will decline in strength unless there is a variation in the stimulus. Therefore, keep up the power of concentration by either changing the object you are observing; or else by discovering some new properties, qualities or attributes in it. (3) The things you wish to shut out of consciousness can best be shut out by your concentration upon some other thing--the attention can dwell only upon one thing at a time, if focused upon that one thing. (4) The power of applying your attention, steady and undissipated, to a single object, is a mark of strong will and superior mental discipline--weak-minds cannot do this. Therefore, in cultivating concentrated attention you are really strengthening your mind and will.