(After stating the foregoing facts.)
1. Exception is taken to the reference of the case to an auditor. The action was ex contractu for the breach of a contract, and an item of damages depended upon the ascertainment of the amount claimed on the sewerage system, fixed in the contract at five per cent, of the net cost of construction. This required an examination into the cost of construction of that improvement. The statute provides that in all cases in the superior court involving *303matters of account the judge may appoint an auditor to investigate such matters of account and report the result to the court. Civil Code (1910), § 5138. The discretion of the judge in referring a ease to an audtor will not be interfered with, unless abused. Martin v. Foley, 82 Ga. 552 (9 S. E. 532); Teasley v. Bradley, 120 Ga. 373 (47 S. E. 925).
There is another reason why the order of reference will not be held improper in this case. To the plaintiff’s action the defendant filed a plea of set-off. In this plea it was alleged, that in March, 1909, the defendant entered into a contract with the plaintiff, whereby the latter was to prepare plans and specifications for and to superintend the construction of certain paving' in the City of Gainesville; that the plaintiff represented to the defendant that he was a skilled engineer, and had experience, and possessed valuable professional knowledge in that kind of construction work; that under these representations he was employed to do the work, the defendant relying upon his skill and ability to have the improvement done in a skillful and satisfactory manner; that the plaintiff employed an engineer who made his surveys in an unskillful manner, and upon the plaintiff’s attention being called to the engineer’s defective work the defendant was informed by the plaintiff that the complaints were unfounded; that the plaintiff allowed the contractor employed by the city to do his work in an unworkmanlike manner and to use inferior material; and that the plaintiff with full knowledge of these facts permitted him to do the work in this manner and consented thereto. After pointing out the defects in the paving, it was averred that the plaintiff had injured and damaged the defendant, by failure to comply with his contract, in the sum of $1,000; and it was prayed that this amount be set off against the plaintiff’s demand, and that the defendant have judgment for the same. The plaintiff demurred to the plea of set-off, on the ground that it set forth a tort, which could not be pleaded as a set-off in a suit based upon a contract. The pleadings were in this state when the case was referred to the auditor. The defendant voluntarily amended its plea by alleging that the plaintiff was insolvent and would not be able to respond to the defendant if it were forced to sue in another and different court and obtain a judgment, and that the defendant would be remediless unless allowed to set off its claim for the plaintiff’s breach of his eon-*304tract with the defendant against the plaintiff’s alleged claim. Thereupon the auditor ruled that the amendment cured the defect in the original plea. The gist of the plea of set-off was not a failure to perform the contract, but a failure of his duties arising from the contract. The substance of the complaint is that the plaintiff, when his attention was called to the negligent work of the superintendent in making the surveys, permitted it to be done in an unskillful manner; and that, with a knowledge that the contractor employed by the city was imposing upon the municipality inferior work and inferior material, the plaintiff permitted it to be done. The subject-matter of the set-off arose in tort, and the tort was based upon a failure to perform the duties arising out of the contract. Owens v. Nichols, 139 Ga. 475 (77 S. E. 635) ; City & Suburban Railway of Savannah v. Brauss, 70 Ga. 368; Boorman v. Brown, 2 Gale & D. (Q. B.) 793; Flint & Walling Mfg. Co. v. Beckett, 167 Ind. 491 (79 N. E. 503, 12 L. R. A. (N. S.) 924). The damages arising from the alleged misfeasance of the plaintiff in the discharge of his duties arising from the paving contract could not be set off against the present cause of action, except in equity. Damages arising ex delicto can not be set off against a cause of action arising ex contractu; but a defendant sued at law upon, a cause of action arising ex contractu may in equity set off damages arising ex delicto, when the plaintiff is insolvent or anon-resident. Arnold v. Carter, 125 Ga. 319 (54 S. E. 177). The original plea did not allege the plaintiff’s insolvency; but upon this defect being pointed out by demurrer, it was cured by amendment. The plea then became one of equitable set-off, and its result was to make the cause one in equity. It was not merely a defense to the plaintiff’s action, and its purpose was not confined to the defeat of that action. It brought to the court matters outside, and sought the administration of relief, to wit, the allowance of an equitable set-off which could be granted only in the exercise of the equitable powers of the court, the effect of which was to convert the action into an equitable one. Melson v. Dickson, 63 Ga. 682 (36 Am. R. 128); Austin v. Southern Home Ass’n, 122 Ga. 439, 448 (50 S. E. 382). An equitable cause may be referred in whole or in part to an auditor to investigate and report the result to the court. Civil Code (1910), § 5127. And for this reason also we do not think the case was improperly referred to an auditor.
*3052. A motion was made to recommit the report on the ground of certain alleged inconsistencies, and because the findings of the auditor were not supported by the evidence. We do not agree to the criticisms that there were inconsistencies in the findings of the auditor, or that his findings were without evidence to support them; and we do not think the court erred in refusing the motion to recommit.
3. As has been pointed out, this was an equity cause, and it was not error to refuse to submit to a jury the exceptions of fact disapproved. In an equity cause exceptions of fact to an auditor’s report are to be submitted to a jury only when approved by the court. Where the evidence, though conflicting, supports the finding of the auditor, it is not an abuse of discretion to disapprove the exceptions of fact. Peyton v. McMillan, ante, 179 (88 S. E. 937).
4. The pivotal question before the auditor was the terms of the plaintiff’s contract of employment by the city. The plaintiff personally appeared before the mayor and council in session and made a proposal for the contemplated improvements. After hearing from him the following resolution was passed, and entered on the minutes: “On motion council voted to employ Mr. H. S. Jandon as engineer to take this work in hand and superintend the same during its construction and until the same is finished — water-plant and extension of water-mains, and to pay him for same the sum of $3,250 and 5 per cent, on the net cost of all sewer work done by him.” The auditor found that the plaintiff expressly accepted the employment under the terms of the ordinance, and actually did work in pursuance of the contract therein expressed. The defendant filed a plea to the effect that the resolution as passed by the mayor and council was to be effective only if bonds carried; and that if bonds did not carry, or if the plaintiff did nothing more than the preliminary work, he was to receive the sum of $300 and nothing more for that service. It further pleaded that the resolution was passed with the understanding that these terms were a part of the contract of employment, and that they were omitted from the minutes by accident and inadvertence. As to this plea the auditor reported that it was demurred to orally, but that he reserved his decision to hear the evidence, which he found was insufficient to sustain it. It further appeared that bonds were au*306thorized by popular vote; and a bond commission, to expend the proceeds was created by ordinance, and not by legislative action. Various exceptions deal with the rulings of the auditor upon this point. A resolution of a municipality may bind the corporation as a contract when so intended. People v. San Francisco, 27 Cal. 665; Wade v. Newbern, 77 N. C. 460; 20 Am. & Eng. Enc. Law, 1161; 28 Cyc. 667. The evidence before the auditor authorized a finding that the city’s obligation to pay the plaintiff the amount expressed in the resolution was not contingent or conditional, as contended for by the defendant; and that such condition was not omitted from the minutes by fraud, accident, or mistake. The obligation of the city as expressed in the ordinance was to pay the amount therein fixed, and the municipality will not be allowed to impeach its minutes, and impair the obligation which it creates, by showing that the contract of employment was conditional, in the absence of fraud, accident, or mistake.
5. The court sustained exceptions of fact which went to the allowance of $675 for sewer work, and eliminated that from the recovery, and rendered judgment in accordance with the report of the auditor, as thus modified, as follows: “That plaintiff recover of defendant the sum of twenty-two hundred and fifty dollars ($2250.00) principal, and the sum of ($723.33) seven hundred and twenty-three 33/100 dollars interest to this date, aggregating $2973.33, and the sum of........cost of court.” The auditor did not report any finding of interest, and there is no exception to the judgment of the court as to interest, other than as contained in the general exception to the final decree, that the court “erred in allowing said order and judgment to be rendered, because it was contrary to law and to the evidence.” Where exceptions of fact are approved, it is the duty of the court to submit the issue formed by the exceptions to the jury. The plaintiff in error, however, can not complain of the court’s eliminating from the finding of the auditor the allowance for sewer work; and there is no complaint on the part of the defendant in error as to the action of the court in this particular. It is argued in the brief that the judgment should be reversed because the interest recovered in the judgment is an incorrect charge. The exception that the judgment was “contrary to law and to the evidence,” treated as a specific exception to the final judgment, is insufficient; because the rule is well *307settled that if exception is taken to the final judgment as being erroneous in itself, an assignment of error should specifically set forth the error or errors which are complained of. Lyndon v. Georgia Ry. & El. Co., 129 Ga. 353 (58 S. E. 1047). If the plaintiff in error desired to raise the point that interest was not recoverable, or that the amount allowed by the court was excessive, or that interest was not recoverable eo nomine, it should have plainly specified the grounds upon which it contended the judgment was erroneous in this respect. Having failed to do this, we hold there is no proper assignment of error upon which the propriety of the allowance of interest can be reviewed by this court.
6. Exceptions were taken to the numerous rulings of the auditor on the admissibility of evidence, and as to certain abstract questions of law. There was no substantial error in any of these rulings of which the plaintiff in error complained; and as the finding of the auditor has the approval of the trial court) and upon an inspection there is ample evidence to sustain the judgment as rendered by the court on the auditor’s report, the judgment is affirmed.
Judgment affirmed.
All the Justices concur.