It is obvious that authority to send an answer by mail must be limited to an acceptance properly addressed.15 And as the postal laws of the United States require entire or partial prepayment of postage, a letter of acceptance mailed without a stamp will not create a contract.16 But as letters with the minimum requirement of stamps upon them are sent forward, though their weight is such as to require additional postage, it is not so clear that an acceptance thus stamped is not effective when mailed.17 That prepayment of a telegraphic acceptance is essential does not seem probable, since no added risk of delay or of failure to reach its destination is involved. The question may also be suggested whether a contract could be completed by mailing a letter of acceptance at a time when mails were stopped by disturbance of nature, by riots, or by war; and, similarly, whether dispatching a telegraphic acceptance would be sufficient if telegraphic communication had been interupted by breaking of the wires. Certainly if the acceptor knew of the circumstances, no contract ought to be held to have been formed.18 If the acceptor had no reason to know of the interruption, it would seem that since the offeror has authorized the means of communication adopted, he must take the risks which that method of communication involves.