Take a homely example. The baker mixes exactly the right quantities of flour, salt, and yeast with water, and then places the dough which he has made in an oven heated to just the right temperature, and produces a loaf of bread. Why? Because the conditions were good ones. Had he omitted the flour, the yeast, or the water, or had he used an oven over or under-heated, he could not have produced an eatable loaf of bread, because the conditions made it impossible. This is what is meant by the terms "good conditions," "bad conditions," "breaking conditions." The conditions, then, under which I have been able to prove to many hundreds of inquirers that it is possible for materialized entities to appear on earth, in solid tangible form, are these: First, light, of suitable wave-length, i.e. suitable color, and let me say here, once and for all, that I have proved conclusively for myself that _darkness is not necessary_, provided that one is experimenting with a sensitive who has been trained to sit always in the light. On two occasions I have witnessed materializations in daylight; and neither of Sir William Crookes's sensitives--D. D. Home or Florrie Cook (Mrs. Corner)--would ever sit in darkness, the latter--with whom I carried out a long series of experiments--invariably stipulating that a good light should be used during the whole time that the experiment lasted, as she was terrified at the mere thought of darkness. I find that sunlight, electric light, gas, colza oil, and paraffine are all apt to check the production of the phenomena unless filtered through canary-yellow, orange, red linen or paper--just as they are filtered for photographic purposes--owing to the violent action of the actinic (blue) rays which they contain (the rays from the violet end of the spectrum), which are said to work at about six hundred billions of vibrations per second. But if the light is filtered in the way that I have described, the production of the phenomena will commence at once, the vibrations of the interfering rays being reduced, it is said, to about four hundred billions per second or less. In dealing with materializations we are apt to overlook the fact that we are investigating forces or modes of energy far more delicate than electricity, for instance. Heat, electricity, and light, as Sir William Crookes tells us, are all closely related; we know the awful power of heat and electricity, but are only too apt to forget--especially if it suits our purpose to do so--that light too has enormous dynamic potency; its vibrations being said to travel in space at the incredible speed of twelve million miles a minute;[15] and it is therefore only reasonable to assume that the power of these vibrations may be sufficient to interfere seriously with the more subtle forces, such as those which we are now investigating. [Footnote 15: 186,900 miles a second (J. Wallace Stewart, B.Sc.).]