Physiognomy is "the science and art of discovering or reading the temper and other characteristic qualities of the mind by the features of the face." The philosophy underlying the science of Physiognomy has been stated at length in the first several chapters of this book, the essence of which is that _mental states manifest in outward form_. The majority of persons apply the principles of Physiognomy more or less unconsciously in judging the characters of those with whom they come in contact. Nearly every one scans closely the features of those whom they meet for the first time, and form a general impression therefrom. Children and domestic animals possess an instinctive knowledge of facial expression and can often tell very accurately the general disposition toward them possessed by various persons. Certain persons are generally considered to "look stupid," while others have "a bright, intelligent expression"; some look "tricky," while others "look honest" and trustworthy. Professor Nelson Sizer says: "Though all human beings have the general human form and features--though all have eyes, nose, mouth, chin, etc., yet each one has a different face and look from every other. And, more, yet, the same person has a very different facial look at different times, according as he is angry or friendly, etc. And always the same look when in the same mood. Of course, then, something causes this expression--especially, since all who are angry, friendly, etc., have one general or similar expression; that is, one look expresses anger, another affection, another devotion, another kindness, etc. And since nature always works by means, she must needs have her physiognomical tools. Nor are they under the control of the will, for they act spontaneously. We cannot help, whether we will or no, laughing when merry, even though in church, pouting when provoked, and expressing all our mental operations, down even to the very innermost recesses of our souls, in and by our countenances. And with more minuteness and completeness than by words, especially when the expressions are intense or peculiar."