If the power designates a place of sale, that is the expression of the owner's will, and the agent is bound to observe it. An authority to sell "at once" could not be extended to invest the agent with authority to sell some time in the future.18 So where the authority to sell is limited to thirty days, the agent would be bound to sell, if at all, within that time. The principal may, or may not have a reason for investing the power with limitations, but in any event the express limitations put on the power will protect the principal.19