There is, however, a good way of using this instrument to get what you want, and that is to perform the whole operation in a consecrated circle, so that undesirable aliens cannot interfere with it. You should then employ the proper magical invocation in order to get into your circle just the one spirit you want. It is comparatively easy to do this. A few simple instructions are all that is necessary, and I shall be pleased to give these, free of charge, to any one who cares to apply.