When the defendant employed the plaintiff to buy cotton on his account in the New Orleans market and to ship it to Boston, he is "presumed to have contemplated that the purchases would be made in the ordinary course of such business at that port. Upon the question whether the plaintiff is liable in damages for negligently or improperly executing such a commission, the evidence of the usages of the cotton trade were clearly admissible, especially as it appears that the defendant himself was well acquainted with them. The employment of a broker to effect the purchases was a justifiable delegation of authority to a sub-agent, because this manner of transacting business was the usual and known custom of the New Orleans market. The statement that the seller of the cotton is understood to warrant that the cotton is sound at the time of sale seems to have been a part of the narrative given by the witnesses of the course of the business; and not an attempt to prove by custom a warranty in a case where none would be implied by law.

In a business which requires or justifies the delegation of an agent’s authority to a sub-agent, who is not his own servant, the original agent is not liable for the errors or misconduct of the sub-agent if he has used due care in his selection. The instructions of the presiding judge appear to have been conformable to law, and well adapted to the case disclosed by the bill of exceptions.

But upon the question whether the plaintiff was guilty of negligence in buying cotton which had been wet by rain before it was purchased, or in suffering the cotton to be rained upon while it was in his custody and care, evidence was introduced, as we think improperly, that other cotton which arrived on other steamers about the same time with this lot had been wet by rain. Much better evidence existed of the state of the weather at New Orleans when this cotton was shipped. The other lots may have been wet before this was purchased, or on the voyage. It was not competent for the purpose for which it appears to have been allowed to be introduced

*508And we cannot say that it was merely immaterial, and not calculated to prejudice the defendant. On the contrary, we think it had a tendency to mislead the jury upon the real issue whether the plaintiff had been guilty of negligence in the execution of his agency. The jury would naturally consider the fact that other cotton arriving about the same time had been rained upon, as a circumstance tending to show that this cotton also was wet by rain without the fault of the plaintiff. For this reason only the exceptions are sustained.