Weston J.

The first witness, offered by the defendants, was . admitted as competent, notwithstanding the interest attempted to be *54shown by the parol testimony objected to by them. The interest is nothing more, than every surety has in the solvency and ability of his principal; or a creditor in that of his debtor. It is an interest going to his credibility. But the fact from which it arises, like every other fact proved in the trial of a cause, should not be made out from testimony liable to legal objection. And if the parol testimony received to prove the interest of the witness was of this character, the verdict cannot be supported. The examination of the witness to ascertain his interest, was in effect upon the voir dire. It was a preliminary inquiry, not a part of the issue on trial, which is to be proved by the best evidence; a rule well known, and with which every party is, or ought to be, prepared to comply. But an objection to a witness on the ground of interest, is often unexpectedly made. Neither the witness therefore, nor the party producing him, can be reasonably required to have with them written papers or documents, which may happen to be referred to upon such an inquiry. The witness is to make true answers to such questions as may be put to him ; and his mouth is not to be stopped, as to any fact within his knowledge, by a technical rule, which is altogether just and proper, with respect to facts involved in the issue. Has he given a note ? Has he given a deed ? Is he a member of a certain corporation ?— Doubtless the production of the note, the deed, and the books of the corporation, would be the best evidence of these facts. But they are within tire knowledge of the witness ; and the party objecting has a right to appeal to him upon the voir dire. A different rule would not only be unnecessary, but exceedingly inconvenient in practice, as it would occasion the delay or the continuance of a cause from time to time, as objections of this sort might successively arise, in the progress of a trial. It is laid down in the text of Starlcie on evidence, part 1, 121, and part 2, 756, that a witness upon the voir dire, may be examined as to the contents of documents not produced. If however the witness produces the written document upon the voir dire, it must be read. Butler v. Carver, 2 Starkie’s cases, 433. But the exception proves the rule ; which was in that case admitted to exist. And we are of opinion the testimony objected to was admissible.

*55By the common law, the estimation of damages is within the province of the jury. Courts may, and often do, in cases of manifest excess, interfere by granting a now trial. Where the injury affects the personal feelings, this is rarely done. And in cases of fraud or wanton trespass, considerable latitude has been allowed. But where títere- exists a fixed standard or scale, by which damages may be calculated, a jury will not be permitted to depart from it. Thus assumpsit, instead of debt, is now the remedy universally resorted to, upon simple contracts for the payment of money. By the form of the action, damages are sought for the nonperformance ; hut the measure of damages is the debt due, with interest for the detention, for a longer or shorter period, according to circumstances. In other cases, arising from the nonperformance of agreements, the standard is less definite ; and necessarily attended with greater uncertainty. In general, the delinquent party is holden to make good the loss occasioned by Ms delinquency. But his liability is limited to direct damages, which, according to the nature of the subject, may he contemplated or presumed to result from his failure. Remote or speculative damages, although susceptible of proof, and deducible from the nonperformance, a .re not allowed.

And if the party injured has it in his power to take measures, by which his loss may be less aggravated, this will be expected of him. Thus in a contract of assurance, where the assured may be entitled to recover for a total loss, lie, or the master employed by him, becomes the agent of the assurer to save and turn to the best account, such of the property assured, as can he preserved.

The purchaser of perishable goods at auction, fails to complete his contract. What shall be done ? Shall the auctioneer leave the goods to perish, and throw the entire loss upon the purchaser r That would be to aggravate it unreasonably and unnecessarily. It is his duty to sell them a second time, and if they bring less, he may recover the difference, with commissions and other expenses of resale, from the first purchaser.

If the party entitled to the benefit of a contract, can protect himself from a loss, arising from a breach at a trifling expense, or with reasonable exertions, lie fails in social duty, if he omits to do so, re*56gardless of the increased amount of damages, for which he may intend to hoid the other contracting party liable. Qui non prohibit, cum prohibere possit, jubet. And he who has it in his power to prevent an injury to his neighbor, and does not exercise it, is often in a moral, if not in a legal point of view, accountable for it: The law will not permit him to throw a loss, resulting from a damage to himself, upon another, arising from causes for which tire latter may be responsible, which the party sustaining the damage, might by ■common prudence have prevented. For example j a party contracts for a quantity of bricks to build a house, to be delivered at a given time; and engages masons and carpenters to go on with the work. The bricks are not delivered. If other bricks of an equal quality, and for the stipulated price, can be at once purchased on the spot, it would be unreasonable, by neglecting to make the purchase, to claim and receive of the delinquent party, damages for the workmen, and the amount of rent, which might be obtained for the house, if it had been built. The party, who is not chargeable with a violation of his contract, should do the best he can in such ■cases, and for any unavoidable loss occasioned by the failure of the ■other, he is justly entitled to a liberal and complete indemnity.

The instruction's of the judge to the jury objected to by the counsel for the defendants at the trial, were in conformity with these principles, and in the opinion of the court not liable to legal objection. Judgment on the verdict.