Upon this belief many erroneous, superstitious and dangerous systems of philosophy and religion were established. The natural philosophy of Baptista Porta, or Albertus Magnus, was founded upon the principle of sympathy. Plato applied this principle to marriage, and maintained that "marriage was the union of two souls that once, in their preexistent state, were one, and that sympathy urges them to union again, and sends them unconsciously seeking it over the world." In the middle ages it was maintained that two friends could be so moved with mutual sympathy as to have, under certain conditions, a true and perfect knowledge of one another's state, even when at a great distance apart. To the revival of this erroneous view of the law of sympathy may be ascribed the theories of Mesmerism and spiritual rappings at the present day. Home-sympathy, viewed as a feeling and a faculty, is twofold in its nature, viz., passive and active. As passive, it is the mere sense of harmony of feeling among all the members, producing the idea and feeling of the oneness of home. It makes a unity of affection, so that the temper, hopes and interests of each member have a living echo and response in all the others. It gives to home its unitive heart, preserves its vital coherence, fuses all the hearts together, makes each a thread in the web of home-being, where each finds its true measure, is inspired with the home-feeling when all is right, and oppressed with home-sickness when separated from it. But home-sympathy is also active. As such it is "the active power that one person has naturally of entering into the feelings of another, and being himself affected as that other is." Each member of home has the power in his feelings of making the feelings of all the other members his own, though he may not have the causes of the feelings of the one with whom he sympathizes. Thus one friend may feel the grief of another, actually and really, though he may not suffer the loss of that friend. He can make the emotion which that loss caused, his own. We may weep with the mother who pours her floods of anguish upon the grave of her child, though we may not have sustained the same loss. The husband weeps with his wife, though he may not be able to feel the pangs which penetrate her heart. The child can enter into the feelings of the parent, and be affected to tears or to joy by them. And thus the home-sympathy demands that all the emotions of home, whether joyful or painful, must affect all,--must vibrate from heart to heart. It involves the power of home-transference, by which, each member conveys to his own affections, all within home. It is thus the law of adaptation and assimilation, for the home-affections. In obedience to this law the hearts and interests of the members are bound up in beautiful harmony. The necessities of one are supplied by all. It is this which makes the members faithful to each other, and prompts them to deeds of disinterested love.