This is a petition for a writ of certiorari. The petitioner demurred to the return. The demurrer was overruled and an order was made that the petition be dismissed. The questions of law thus raised were reported for our determination.
The case relates to taxes assessed upon property of the Westport Manufacturing Company in the town of Westport. The company applied for abatement and upon denial by the assessors appealed' to the county commissioners under G. L. c. 59, § 64. The property in question consisted of a manufacturing establishment whose buildings and machinery were old. The power for the operation of the plant was furnished chiefly by steam and partly by the development of the water power of a stream on which it was located.
*562The only matter presented for consideration on a petition for a writ of certiorari is the correction of substantial errors of law apparent on the record of an inferior tribunal whose course of procedure is not according to the common law. Findings of fact are not open to review or revision. Hogan v. Collins, 183 Mass. 43, 46. Swan v. Justices of the Superior Court, 222 Mass. 542, 546. The question to be determined is whether the return of the respondents shows such harmful error of law as to satisfy us that substantial justice requires the writ to issue. Haven v. County Commissioners, 155 Mass. 467.
It is not contended that the respondents did not follow the correct rule of law in its abstract statement for determining the value for taxation purposes of the property in question. The rule they adopted was sufficiently favorable to the petitioner. Massachusetts General Hospital v. Belmont, 233 Mass. 190, and cases there reviewed; S. C. 238 Mass. 396, 402. Compare Boston v. Lawrence, 119 Mass. 126, 128, 132. Smith v. Commonwealth, 210 Mass. 259.
The several grounds of demurrer to the return were overruled rightly. A report of the evidence in support of the findings of fact in whole or in its different parts formed no proper part of the return of the respondents, would have been irregular and would have been an unnecessary encumbrance of the record. Farmington River Water Power Co. v. County Commissioners, 112 Mass. 206, 217. It does not appear that any question of law was raised at the hearing before the county commissioners as to any one of the several matters of law set forth in the demurrer. In any event they are without merit.
The return of the respondents shows that no exception was taken to any evidence introduced at the hearing before them. It is now argued that the testimony of two witnesses was inadmissible and should have been disregarded. That contention cannot be sustained. These witnesses testified as experts. Their qualifications in this particular cannot now be successfully assailed. Stein v. Strathmore Worsted Mills, 221 Mass. 86, 90. No objection was made to their testimony at the time. It was too late after the witnesses *563were dismissed to raise questions as to the competency of their evidence. Orpin v. Morrison, 230 Mass. 529, 532.
No error of law was shown, treating the point as broadly as has been argued by the petitioners. The element of water power in connection with mill property is not a distinct and independent item of property but is to be considered as affecting the value of the real estate. Essex Co. v. Lawrence, 214 Mass. 79, 89, 90.
The testimony now attacked cannot be said to have been of such nature as to render it valueless. The amount and cost of steam power saved by the use of water for the production of power was a factor which might have been considered in reaching an estimate of value. If in the opinion of these witnesses that was its only value as a part of the cash value of the whole property, their testimony was not on that account of no value as matter of law. Lakeside Manuf. Co. v. Worcester, 186 Mass. 552. Sargent v. Merrimac, 196 Mass. 171.
The view taken by the respondents may have given them a conception of fair cash value of the property. In a hearing to determine fair cash value for the purposes of taxation, the view by a tribunal like county commissioners, presumably composed of practical men somewhat experienced by virtue of their office in estimation of land values, cannot be said to furnish no basis for estimation of value. Parks v. Boston, 15 Pick. 198, 209. Smith v. Morse, 148 Mass. 407, 410. Commonwealth v. Dascalakis, ante, 12, 29, 30, 31, and cases there cited.
There is nothing in this record which under well settled . principles requires the issuance of the writ.
Demurrer overruled.
Petition dismissed.