Agency by [or of] necessity

What does Agency by [or of] necessity mean in American Law?

The definition of Agency by [or of] necessity in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

An agency, i.e., a power to bind another, given as a matter of law to some persons in some circumstances, e.g., a dependent, deserted or ignored spouse may have the power to buy goods requisite to decent survival and bindingly charge the cost to the absent spouse. Also, an agent may have “agency by necessity” to go beyond his actual authority in an emergency e.g., in his principal’s absence to order a ship to leave a port about to be embargoed. This “agency by necessity” is sometimes called an

implied agency resting on implied authority. That, however, is just confusing; “implied” should be reserved for things implied in fact, whereas this agency by necessity is nothing more than a rule of law imposing powers and duties regardless of anyone’s factual concurrence.