108. We will conclude our examination of this part of our subject, by a reference to an optical effect which has given rise to the singular hypothesis of globular spirits.

The air is not always absolutely limpid; and its molecules when rarified by heat often become visible. Some people have taken this rarified air for a mass of spirits fluttering in space! - We allude to this opinion only as an absurdity. Another opinion, equally absurd is that spirits can be seen in the opaque specks which are sometimes formed in the aqueous humour of the eye, and which, being held in suspension in the liquid of which they follow the movements, assume the appearance of minute disks that seem to float in the atmosphere. We have seen persons who have taken these disks for spirits, following and accompanying them everywhere; a fancy about as rational as that which sees a man in the moon. Others again have taken the black films that are sometimes seen in the eye for evil spirits.

Illusions of every kind can only result from superficial observation. A careful study of the nature of spirits, with the aid of the means that practical Spiritism affords us, will enable the inquirer to keep clear of hasty and fanciful inductions, while enlightening him in regard to the reality of spirit-manifestations. Just as it is the duty of every spiritist to combat the erroneous judgements which are based on ignorance of the latter, it is also his duty to combat the erroneous suppositions suggested by unreasoning enthusiasm, and which cannot fail to render Spiritism ridiculous in the eyes of those who are acquainted with it only through the fanciful exaggerations of some of its adherents.

109. The perispirit, as we have seen, is the foundation of all spirit manifestations, to which the knowledge of this integral part of a spirit's personality gives us the key; a key which, let us never forget, has been furnished by the spirits themselves, for it is by them that the existence, nature, and functions of the perispirit have been made known to us. This knowledge enables us to understand the action of spirits on matter, the movement of inert bodies, the mode of production of aural, visual, and tangible phenomena; it will also be found equally available for the explanation of the other phenomena which we shall have to examine, before we proceed to the study of spirit-communications properly so-called, and which we shall comprehend all the more easily with the aid of the preliminary knowledge we shall thus have acquired of the general principles on which they rest.

110. We are far from regarding the theory which we are about to set forth, as being absolutely true in every minute particular, or as giving an exhaustive explanation of the subjects which it deals. The instructions we have already derived from our spirit teachers will doubtless be completed or rectified by future studies; but, however incomplete or imperfect our theory at this time, it will at least assist us to comprehend the possibility of certain facts, by showing that they result from the action of natural causes, and are therefore in no way supernatural. Regarded as a hypothesis, it is one the reasonableness and probability of which cannot be denied, and which may fairly claim to be worth all the arguments employed by our opponents to prove that there is nothing but illusion, phantasmagoria, and deception, in spirit phenomena.