But, then, there is the visible body of the spirit—what is that, and how does it retain its shape?—for we know that there is a law (discovered by Dalton) that two masses of gaseous matter can not remain in contact, but they will immediately proceed to diffuse themselves into one another; and accordingly, it may be advanced that a gaseous corporeity in the atmosphere is an impossibility, because it could not retain its form, but would inevitably be dissolved away, and blend with the surrounding air. But precisely the same objection might be made by a chemist to the possibility of our fleshly bodies retaining their integrity and compactness: for the human body, taken as a whole, is known to be an impossible chemical compound, except for the vitality which upholds it; and no sooner is life withdrawn from it, than it crumbles into putrescence; and it is undeniable that the aeriform body would be an impossible mechanical phenomenon, but for the vitality which, we are entitled to suppose, may uphold it. But, just as the state or condition of organization protects the fleshly body from the natural reactions which would destroy it, so may an analogous condition of organization protect a spiritual ethereal body from the destructive influence of the mutual interdiffusion of gases. Thus, supposing this aeriform body to be a permanent appurtenance of the spirit, we see how it may subsist and retain its integrity; and it would be as reasonable to hope to exclude the electric fluid by walls or doors as to exclude by them this subtle, fluent form. If, on the contrary, the shape be only one constructed out of the atmosphere by an act of will, the same act of will, which is a vital force, will preserve it entire, until, the will being withdrawn, it dissolves away. In either case, the moment the will or thought of the spirit is elsewhere, it is gone—it has vanished. For those who prefer the other hypothesis—namely, that there is no outstanding shape at all, but that the will of the spirit, acting on the constructive imagination of the seer, enables him to conceive the form, as the spirit itself conceives of it—there can be no difficulty in understanding that the becoming invisible will depend merely on a similar act of will. CHAPTER XIII. HAUNTED HOUSES.