28. Although invisible to us in its normal state, the perispirit is ethereal matter, nonetheless. In certain cases, the spirit can undergo a sort of molecular modification that renders it visible and even tangible; this is how apparitions are produced. This phenomenon is no more extraordinary than steam, which is invisible when it is extremely rarified, but which becomes visible when it is condensed.
Spirits who make themselves visible nearly always appear as they did while alive so that they can be recognized.