This case was originally argued at Harrisburg, on the 3d of June 1876, Sharswood and Williams, JJ., being absent. An opinion therein ivas delivered by Gordon, J., on the 6th of November following, affirming the judgment. On the 24th of the same month the plaintiffs in error asked for a re-argument, which on the same day was ordered, Mercur and Gordon, JJ., dissenting. The case was re-argued on the 26th of February 1877, by the same counsel, and *523on the 7th of May 1877 Mr. Justice Sharswood delivered the following opinion:—
We are of opinion that there was error in the rejection of the evidence which forms the ground of complaint in the first assignment.
It appears that on the 22d April 1870, the plaintiffs in error advertised for proposals to be received on the 7th of May following, for the erection of a bridge of wrought iron over the river Schuylkill, near Monocacy Furnace. According to, the terms of this advertisement the bridge was “ to be of sufficient strength and warranted to carrry a load of one ton to each lineal foot. Proposals to specify the greatest strain per square inch in pounds, to which the metal will be subjected in sustaining the weight required, viz., one ton to each lineal foot.” Other particulars are specified not necessary to be now referred to. On the 4th of May, the defendants sent in proposals, which, among other things, stated that they would “ guarantee the bridge to bear a rolling load of one ton to the lineal foot.” They add: “The calculation is as follows for the strength of the bridge: 10,000 pounds allowed per square inch for tensile strain, and 8000 pounds for compression strain.” These proposals were accepted. On the 7th of May the contract was executed, which provided, so far as is material to the question now before us, that the structure was “ to be built and erected in a good, workmanlike manner and of good materials, and is to be completed and ready for use on or before the 1st day of November, A. D. 1870, in accordance with annexed specifications.”- The only specification annexed was a printed copy of the advertisement for proposals. It is plain that the annexing of this advertisement instead of the proposals or a specification drawn up from them was a mistake. The reference in it to the proposals made them a part of it, and the fact that they were to be in the future is explained by the date of the advertisement, and that they were to be received on the 7th of May, the day of the date of the contract. The proposals should have been received in evidence. The parol evidence, that the president of the Bridge Manufacturing Co., the corporation of the defendants, appeared before'the plaintiffs’ board before the award of the contract, and explained the written proposal, and that it was upon that basis the contract was awarded and the agreement entered into, was competent and ought to have been admitted. It infringed no rule which has ever been laid down on the subject of parol evidence to vary written instruments. It did not vary the agreement. It only rendered complete what was apparently deficient on its face. The paper annexed to the agreement as a specification was manifestly incomplete without the proposal, and it required the parol evidence to show that the proposals were in- point of fact the basis of the contract. The - case scarcely requires a resort to the well-established principle that parol evidence can always be given to *524prove mistake in a written contract, but, if it does, that rule fully covers it. But, in truth, the offer was not to vary the agreement by evidence of a mistake, but to identify and prove a paper which was a part of and incorporated in it by the reference in the specification.
The second and third 'assignments of error are not sustained. The declarations and admissions of Moseley were not within the scope of his authority, which was merely to make a settlement with the plaintiffs. As to the fourth and fifth assignments, the questions proposed to be asked of the witness Wright were not sufficiently specific to justify us in convicting the learned court of error in not allowing them to be put. The witness was not ah expert, and though there are many things palpable to the senses which it does not require an expert to prove, yet in this case the questions should have been so framed as not to involve in the answers opinions which none but an expert would be competent to express. As to the sixth and seventh assignments, no doubt the learned judge would have allowed the questions objected to to be put had the proposals been in evidence. As the case then stood upon the evidence there was no error in the rejection of them. We find no error in the 8th, 9th, 10th, 11th and 12th assignments, but we think there was good ground to complain of that part of the charge which forms the subject of the thirteenth assignment. Undoubtedly if there has been substantial performance the plaintiffs are entitled to recover, but not necessarily the whole contract price. There may be defects in the fulfilment of such a nature as not to preclude the plaintiffs from recovering, but for which the jury would have a right to make a deduction as a compensation to the defendants.
Judgment reversed, and venire facias de novo awarded.