Under the deed from Bowles and Atwood to Howe and Martin, the defendant has the right to take from the "bulkhead and flume the quantity of water which shall be discharged therefrom through an aperture of two hundred square inches at the gate under fifteen feet head."
Reported cases upon conveyances of water-power show great numbers of controversies arising from the methods adopted by grantors and grantees for ascertaining the quantity of water or power conveyed. The quantity is often described as a capacity to do specified work, or is to be found by tests otherwise open to contention. Johnson v. Rand, 6 N.H. 22; Whittier v. Cocheco Mfg. Co., 9 N.H. 464; Dewey v. Williams, 40 N.H. 222; Bullen v. Runnels, 2 N.H. 255, 262; Loverin v. Walker, 14 N.H. 489, 491; Saunders v. Newman, 1 B. Al. 258. A great variety of phrases are used in such conveyances, that leave the amount of granted or reserved power to be ascertained by experiment or scientific computation. In many cases the quantity of water actually taken at any one time is not apparent upon inspection, and can only be determined by measurements together with difficult and laborious calculations.
All difficulties of this kind the parties to the deed of 1866 attempted to avoid by precise and carefully selected language *Page 272 intended to preclude doubt and litigation. They used expressions that required the construction, maintenance, and use of a conduit and gauge, with a necessary and incidental right of reasonable inspection that would render an infringement of the grantors' rights visible without measurement or computation.
If the height of the water in the plaintiffs' bulkhead and flume were uniform at all seasons, the apparent intention of the parties could easily be carried into effect. "The quantity of water which shall be discharged therefrom through an aperture of two hundred square inches at the gate under fifteen feet head" would not be the quantity that could be discharged through more than one aperture, nor through a larger aperture than two hundred square inches, nor under a greater head than fifteen feet. And the plaintiffs would be entitled to a decree requiring the defendant to construct his works in a form that would give him no means of drawing water through a larger aperture or under a greater head. But the height of water in the bulkhead and the flume is not uniform. It varies as the amount of rain-fall varies in wet and dry seasons. An aperture of exactly two hundred square inches under fifteen feet head in low water would in high water give the defendant more power than was granted by the deed. So an aperture of that size under fifteen feet head in time of flood would give him in time of drought less than was granted. Because the head varies from time to time, a fixed aperture of exactly two hundred square inches will give the defendant more or less than the granted quantity, according as the head is greater or less than fifteen feet. Hence, in order that the defendant may at all times have a power equivalent to a stream of water discharged through an aperture of two hundred square inches under fifteen feet head, the aperture must be enlarged as the head falls, and diminished as it rises.
At the hearing evidence was received on the irrelevant issue of the local meaning of the words "at the gate." Incompetent evidence was received of the uses to which the parties understood the premises were to be put. Usage is admissible to explain what is doubtful, but not to contradict what is plain. 1 Gr. Ev., s. 292. It is not admissible to control a written contract unambiguous in its terms. Potter v. Smith, 103 Mass. 68; Davis v. Galloupe, 111 Mass. 121; Hedden v. Roberts, 134 Mass. 38. At the date of the deed there was no mill on the factory site, and had been none for seventeen years; and the only gate was in the bulkhead or flume.
The deed of 1866 provides for a gate at the aperture, but does not restrict the size of the gate or the size of the wheel. It is for the defendant to determine how large the gate and wheel shall be, how many apertures there shall be in the wheel and their size, and all details of the structure of the wheel. The essential limitation is, that the water he uses shall be discharged before he uses it through an orifice not larger than two hundred square inches *Page 273 under a head of fifteen feet, or its equivalent under a greater or less head. With all the water so obtained he can do what work he pleases in his own way. All the power he loses through wasteful wheels is his loss; all of it that he saves by improved wheels is his gain. Bullen v. Runnels,2 N.H. 255, 266; Dewey v. Williams, 40 N.H. 222; Saunders v. Newman, 1 B. Al. 258. He has every inducement to adopt the mechanical inventions that will obtain the greatest power from a stream discharged through an orifice of the size and under the head fixed in the deed, or its equivalent.
Counsel have argued the question whether fifteen feet head means with the water at rest at the bulkhead, or in motion through the defendant's penstock. From the terms of the deed, executed when there was no mill or penstock on the premises, we infer the parties meant that the grantees' power should be ascertained and set out by measuring from the top of the water at the bulkhead, at rest, till they had a difference of level of fifteen feet.
No evidence was offered to show a latent ambiguity in "head," to be removed by parol evidence; and without any parol evidence on that subject (on the competency of which we express no opinion) we think the parties meant to measure the head when the water was not running through the grantees' penstock, and when there was no penstock there, taking the measure to determine where the penstock should be built and where the aperture should be located. One reason for inferring that this was the intention is, that the water at rest might give a more certain and easily ascertained point to measure from than the uneven surface of the water at the upper end of the penstock when the water is in motion.
At the trial term a commissioner, expert in such matters, must be appointed to determine the location and size of the aperture, and the height to which the gate must be raised at different stages of the water to give the defendant the quantity of water to which he is entitled under the deed. The height to which the gate shall be raised as the level of the water varies should be plainly indicated by marks or figures upon some permanent part of the gate fixtures, open at all times to the inspection of the plaintiffs, that they may readily determine by observation or mere inspection whether the defendant is drawing the quantity of water to which he is entitled, and no more.
The plaintiffs are technically the prevailing party in the equity suit; but as the defendant with his present wheel has not used more water, including the leakages of the penstock, than he would or could have used if it had been drawn through an aperture of two hundred square inches under fifteen feet head before it was used to turn his wheel, no damages can be recovered on that account: nor can the plaintiffs recover damages for his allowing *Page 274 the water to go to waste at night. Neither party is entitled to costs.
Case discharged.
CARPENTER and CHASE, JJ., did not sit: the others concurred.