A private attorney authorized by another to act in his place and stead, either for some particular purpose, as to do a particular act, or for the transaction of business in general, not of a legal character. This authority is conferred by an instrument in writing, called a “letter of attorney,” or more commonly a “power of attorney.” Treat v. Tolman, 113 Fed. 893, 51 C. C. A. 522; Hall v. Sawyer, 47 Barb. (N. Y.) 119; White v. Ferguson, 29 Ind. App. 144, 64 N. E. 49.