The trial of this case was very long. The record before us contains nearly one thousand printed pages. We have carefully examined it, and are satisfied that the findings of the circuit judge upon those questions in the case which are purely questions of fact are amply sustained by the evidence. We shall not discuss them at length. This general statement of our conclusions must suffice.
*423The legal questions at issue are neither numerous nor difficult of statement. Without attempting to quote the language of the findings and judgment in full, it may be briefly stated that the circuit court adjudged, -first, that the term “ square inch of water,” as used in the conveyances in evidence, means “ a volume or stream of water one inch square in cross-section area measured at right angles with the line of its flow, and flowing with the velocity due to the given head; ” second, that the reserved or “ Rig Mill ” water amounted to 3,200 square inches and no more; third, that the several owners of the perpetual use of water have become the sole owners as tenants in common of the dam, canal, and water-power, and all the rights appertaining thereto in the proportion which the number of square inches owned by each bears to 13,532 square inches; fourth, that all the water furnished by the dam has been sold, and that there is no excess over and above the 13,532 square inches which has been sold in parcels. All these findings are challenged by the appellants, Ford and Grossett, who claim that the reserved or “ Big Mill ” water exceeds 3,200 square inches, and that there is an excess of water furnished by the dam over and above 13,532 square inches at a four-foot head, and that they are the owners of a part of each surplus. These contentions will be considered in the order above indicated.
I. As to the meaning of the term “ square inch of water ” It is apparent that the term does not, in the ordinary and usual sense of the words used, convey to the mind any idea of volume. In order to determine what it means it must receive a construction, and the question is, What is the construction or meaning which must be given to it? On behalf of respondents it is claimed, and the circuit court seems to have followed that view,'that the term “square inch of water ” had a definite technical meaning among water engineers and practical mill-men from a time ante*424rior to the making of the first conveyance, and that such meaning was the one found by the court, namely, a stream of water with a cross-section area of one square inch, moving with the velocity due to the given head. On the other hand, it is claimed by appellants that the term had no such definite technical meaning at any time, certainly not in the early days of the water-power in question, and that the meaning of the term as here used must be sought for and found by considering the circumstances and facts surround7 ing the various grants and the evidence of the parties as to the meaning intended by the term, and that in the light of such facts and evidence of intention it must be held that the term means the amount of water which will be discharged through an aperture in a flume of the given number of square inches, the center of which aperture is at the given distance below the surface of the water in the flume. For convenience we will call the first the “ theoretical inch; ” the second, the “ practical inch.”
It appears from the testimony of the experts that there is a considerable difference between the theoretical and the practical inch. The theoretical inch is certain and unvarying.in amount; the practical inch varies in amount according to the construction of the aperture. The practical inch discharged through an aperture with thin edges will measure about sixty-two per cent, in volume of the theoretical inch, but if the aperture be trumpet-shaped, or furnished with proper adjutage inside the reservoir, it may be made to equal the theoretical inch, and even to discharge as much as 240 per cent, of the theoretical inch. The theoretical inch is founded upon a theory, namely, the theory that •water spouting from the side of a flume with a certain head, say four feet, will have the same velocity as if it fell the same distance through the air, and, as this velocity is fixed and certain, the amount of water referred to in the theoretical. inch is fixed and certain. This theory is not *425true in actual practice, for it appears, as has been stated, that the actual discharge through an aperture with thin edges and without adjutage is hut sixty-two per cent, of the theoretical discharge; the reason being that by the crowding together of particles of water coming towards the hole from all directions the flow is retarded, and the stream does not attain its theoretical velocity until it is a short distance outside of the hole where the cross-section area becomes contracted. It is a matter of considerable importance, therefore, which of these meanings is to be applied to the term “ square inch,” as used in the deeds under consideration.
It needs no authority to show that if the term had a fixed and definite meaning among hydraulic engineers and mill-men at the time it was used, such meaning would prevail, notwithstanding the fact that people ordinarily did not know of such meaning, or even that the parties to the deeds themselves did not know of it. Parties cannot use technical terms with a fixed meaning, and then disclaim such meaning. It is equally clear to our minds that when such alleged technical or trade meaning is an arbitrary one, and not a meaning which the word or words would naturally import, it must clearly appear that the acquired or technical meaning was not the subject of dispute or doubt; that it was well settled and understood, at least among members of the profession or trade which is supposed to use the term in such technical sense. It would relieve us of some labor if we were able to say that the testimony here shows that the term “ square inch of water” had acquired the technical meaning embodied in the definition of the theoretical inch at the time of the making of the early deeds upon this water-power, but we are not able to say so. It is true, there are several water engineers who testify that the theoretical inch has become the accepted meaning of the term “ inch of water,” *426but they do not attempt to tell when such meaning became prevalent. There were also some pamphlets called “ wheel books,” which are advertisements issued by makers of water-wheels, which give the technical definition claimed by respondents; but these have all been issued within a few years last past. There was other evidence upon the same side, but, on the other hand, there was much evidence of .practical millwrights, and at least one water engineer, to the effect that such meaning has never obtained or come into general use. The entire testimony on this point forces' upon our minds the conviction that there was not in 1850, or even in 1860, a fixed technical meaning attached to the words such as respondents claim. This impression is strengthened when- we consider a number of decisions in this and other courts where grants of inches of water have been made and defined or explained in the grant by reference to an aperture. Blanchard v. Doering, 21 Wis. 477; Norris v. Showerman, 2 Doug. 16; Schuylkill Nav. Co. v. Moore, 2 Whart. 477. Did the question relate solely to deeds executed within the last decade, the respondents’ argument would be much stronger.
We must, then, seek elsewhere to ascertain the meaning of the words under consideration, as the words were of doubtful signification. Doubtless the circumstances surrounding the parties at the time the grants were made, the condition of the race, the size of the apertures through which water was drawn, the capacities of the wheels used, and many other facts tending to throw light on the apparent intention of the parties at or about the time the deeds were made, should be considered upon the question. Ganson v. Madigan, 15 Wis. 144. There is testimony of this kind in the case, and the appellants claim that it clearly demonstrates that the practical inch is the inch which the deeds should be construed to conve}''. This testimony shows that in some instances the apertures of the wheels proposed *427to be used were measured, and the number of inches granted was fixed thereby, also that among many practical mill-men upon Rock river the term “ square inch ” was understood to mean the area of the aperture. Direct testimony was also given by A. Hyatt Smith that he intended by his grants to measure the inches of water granted by the superficial area of the aperture. This last testimony was, at least, of doubtful admissibility.
Were we left with this testimony alone on the subject, appellants’ contention would indeed be strong. There is, however, other testimony in the case which seems to us of greater significance in the interpretation of all the grants under consideration than that which we have just noticed, and we will briefly state what that evidence is.
In January, 1874, an equitable action was commenced in the United States circuit court for the western district of Wisconsin, by Charles D. Mead, as trustee of the separate estate of Ann M. C. Smith, against Oliver B. Ford and others, being a large majority of the then owners of the water on the power, to restrain the defendants from using more water than the plaintiff claimed they were entitled to use. Oliver B. Ford was the father of the appellants, and their rights came through him. In 1854 A. Hyatt Smith, then owning an undivided three-fourths interest in the dam and canal and the water then unsold, had executed a mortgage to secure payment of a note of $95,000 to Mead as trustee of the separate estate of his wife, Ann M. C. Smith, and it was upon his interest as such mortgage trustee that Mead based his right of action. Answers were served in the action, and in June, 1874, a stipulation was entered into by Mead and a part of the defendants, including Ford, selecting one Hiram F. Mills, a water engineer, as an expert to go to Janesville and make measurements, surveys, and tests, and thereafter to rightly answer interrogatories bearing on the controversy. In pursuance of *428this stipulation Mills made his measurements and answered the interrogatories and filed his report in the latter part of the year 1874. Among those interrogatories was the following: “ What is understood by a square inch of water? ” and to this he answered, “ The square inch of water as it is understood is the square inch of stream of water where the particles are all moving in the same direction as the axis of the stream with the velocity produced by the head.” It will be seen that this is the theoretical square inch. The action was never brought to trial. In fact no further steps seem ever to have been taken. The reason was that in July, 1874, a decree was entered in an action pending in the United States circuit court for the eastern district of Wisconsin, brought by judgment creditors of A. Hyatt Smith, and attacking the Mead trust mortgage as fraudulent, which decree adjudged that the mortgage was void as to such creditors, and that the title still remained in A. Hyatt Smith, and that Smith’s interest be sold by a master to satisfy the claims of such judgment creditors. It cannot be claimed, for obvious reasons, that the Mills report had the effect of an arbitration and award, though no objection or exception seems ever to have been made to it by any of the parties; but the subsequent acts of the parties render it very significant.
In March, 1875, a sale was had by a master in chancery of the interests of A. Hyatt and Ann M.- 0. Smith in the dam and power under the decree in the creditor’s action, and the same was purchased by Oliver B. Ford on behalf of himself and a syndicate of owners of water upon this power and the Monterey water-power below, so that Smith disappeared as an owner of any part of the power.
After this sale, and in August, 1875, an agreement in writing was entered into by all of the then owners of the power, including Oliver B. Ford and Oliver G. Ford, for the purpose of establishing a plan “ whereby the said water*429power, and the use thereof, may be judiciously managed and regulated, to the end that.the rights and interests of the respective parties hereto may be secured and promoted.” This agreement provided that the dam should at once be repaired by a committee appointed, the cost to be apportioned among the owners according to the custom theretofore practiced; that an iron bolt should be placed in the pond above the dam as a watermark below which the water should never be drawn except for the purpose of repairing the dam; that when the water in the river was insufficient to give all the owners the water owned by them (and designated in a schedule attached), then the owners of junior or servient water should cease to draw so much as may be necessary and as shall be designated by the engineer, until the water in the river is again sufficient to supply all; that bulkheads should be constructed at the head of each flume, and a uniform system of gates established at each flume for the delivery of water to each owner, but that if such method be abused by the parties the engineer should have power to regulate the use thereof; and that the engineer should have the right to enter on the premises and buildings of the parties at all times for the purpose'of discharging his duties. Edward Ruger was appointed engineer in charge under the provisions of the agreement.
It will be seen at a glance that this agreement contemplated accurate measurement of the water. The schedules attached gave the number of inches of water owned by each party and the order of priority. It appears without dispute that Edward Ruger acted as engineer under this agreement for four years, and that during that entire time he measured the water and regulated its use under the terms of the agreement; that during the entire time he used as the standard of measurement what we have called the “ theoretical” inch. He says: “In measuring to the owners under these schedules, I gave them a square inch measured *430at right angles with its flow, issuing with the velocity of whatever head was acting upon it. ... I did not at any time measure to them as a square inch of water a volume having a cross-section area less than a full square inch. I never heard any complaint as regards the square inch that they were too large or too small. I do not recollect hearing any complaint of the measurement of a square inch of water as defined by Mr. Mills in his report during the time I was measuring water.” It does not'appear that any different rule was ever used in measuring water to the parties in this case. In fact it would appear that it was never systematically measured and regulated except during the four years that Ruger acted as engineer, and it does not appear that he ceased to act as engineer on account of any dissatisfaction with the standard of measurement used by him. Here, then, during four years, was a practical construction placed by all the parties then interested upon the terms of their conveyances, and the construction so adopted, while technical and arbitrary, possessed the merit of being definite and certain, capable at all times of being ascertained with mathematical accuracy.
It is well settled that the practical construction placed by the parties in interest upon doubtful or ambiguous terms in a contract will exercise great and sometimes controlling influence in determining the construction, and such rule is founded upon manifestly just principles. District of Columbia v. Gallaher, 124 U. S. 505; Topliff v. Topliff, 122 U. S. 121; Pate v. French, 122.Ind. 10; Nilson v. Morse, 52 Wis. 240; Hosmer v. McDonald, 80 Wis. 54. While this rule. applies with greatest force to executory contracts, it is by no means confined to that class, and in this case there is, furthermore, an element partaking of an executory nature in the conveyances, for the water sold is continually being delivered.
We have concluded in this case that the construction' *431which the owners of the power for years placed upon the terms of their grants, it appearing that such construction is reasonable and definite, should and m,ust prevail. We adopt the construction which the parties have adopted, the construction which admits of no doubt as to the amount of water called for, which can always be defined and ascertained with mathematical certainty, and which seems to do justice to all parties in interest, namely, the construction that a “ square inch of water,” as used in the deeds in this case, means what we have termed the “ theoretical square inch.”
II. As to the amount of the reserved or “ Big Mill ” water. As will be noticed by reference to the statement of facts, there was a reservation made in all the early deeds of water upon this power of “ water sufficient, judiciously applied, to drive six run of millstones and necessary machinery.” The language varies somewhat in some of the conveyances, but the differences are not material. This' water was reserved for the use of the “Big Mill,” so called, and by means of the water so reserved the “ Big Mill,” with six run of stone, was operated until its destruction by fire in 1871, after .which time 3,200 inches of such reserved or “ Big Mill ” water have been sold in parcels. If there is any excess over 3,200 inches in this reserved water the appellants are shown to be the owners of one half such surplus, and they contend that the circuit court erred in holding that the amount of the reserved or “Big Mill” water was 3,200 inches and no more.
The doctrine of practical construction is applicable with reference to this reservation as well as with reference to the grant of water. The amount reserved is not definite in amount. Different wheels will use different amounts of -water, and thus the reservation cannot be said upon its face to fix any certain amount of water.
The circuit court found, and the fact seems to be, that *4323,200 square indies of water at a head of four feet is now, and always has been, a sufficient amount to drive six run of millstones and necessary machinery; that the amount of such reservation has always been treated by all the parties interested as 3,200 square inches; that the primary owners at the times when .the various conveyances were executed represented that the amount reserved was 3,200 inches under a head of four feet; that in all the numerous assessments made for repairing or rebuilding the dam and canal, beginning in 1851 and running down to a recent period before this suit was commenced, said reserved water has always been represented by the owners as being 3,200 square inches at a four-foot head, and has always been assessed at 3,200 inches.
Elements of estoppel would seem to be present here as well as practical construction by the parties. We think we need not extend the discussion of this branch of the case. The) circuit court was plainly right in holding that the “ Big Mill ” water is 3,200 inches and no more.
III. As to the ownership of the dam, and as to whether there is any surplus water in the river over and above 13,532 square inches at a head of four feet. These questions are 'closely connected, and may best be considered together. The finding of the circuit court was that the owners of the perpetual use of water have become the sole owners, as tenants in common, of the dam and power, and that all the water furnished by the dam had been sold by the primary owners.
In holding that the owners of water rights are sole owners of the dam the circuit court undoubtedly followed the principle laid down by this court in the case of Smith v. Ford, 48 Wis. 315. The late Mr. Justice Tatlob there says (p. 166) with reference to this same dam and power: “ It seems clear to us that when the original owners had conveyed all the water afforded by the dam, and had re*433lieved themselves from maintaining the same by covenants requiring the grantees to maintain it, such grantees would own the same as tenants in common, each owning such proportion as his quantity of water bore to the whole quantity aiforded by the dam.” If there is any water in the power still unsold, the appellants, as heirs of Oliver B. Ford, are owners of an undivided one-quarter thereof, being the Walker interest, which was deeded to Oliver B. Ford in January, 1874; they also own 2300-4355 of the Smith and Doe three-fourths thereof by virtue of the purchase made at the master’s sale by Oliver B. Ford. The circuit court found, upon conflicting evidence, that the river will supply for continuous use, at its ordinary stage, with its natural volume made uniform by an artificial reservoir called the “ Indian Ford Dam,” from eight to ten thousand square inches of water at a head of four feet, and will not supply more than 13,532 square inches at any time, unless it be for a very short period, during an unusually high stage of water. Undoubtedly, it is the amount furnished at the ordinary stage which must control in determining the capacity of the river, and accepting, as ■ we do, this finding as settling the question as to the amount of water supplied by the river at a four-foot head, it appears at once that the entire amount has been sold, and more.
But it appears that the dam has been maintained for many years at a height which furnishes a head of between seven and eight feet. It is plain that the quantity of water necessary to produce a given amount of power is reduced as the head is increased. By the expert testimony it appears that if we call a square inch of water at a four-foot head one, the fraction of a square inch which will produce the same power under a head of seven feet is .4319. The volume of water in the river is not increased by the raising of the head, but the power furnished is largely increased. Using the rule above quoted, we find that the same power *434produced by 13,532 square inches at a.four-foot head will be produced by 5,84447 square inches at a seven-foot head. The deeds of water uniformly convey a given number of square inches of water at a four-foot head, or water sufficient under any greater head tó he equivalent in power. Under this language it is claimed by appellants that at. a head of seven feet only 5,844.47 inches of water have been conveyed, and the river furnishing, as found by the court, in its ordinary volume, at least 8,000 square inches, there is an unconveyed surplus, a part of which belonged to Oliver B. Ford as grantee of the remaining rights of Walker, the primary owner of one quarter of the dam and power, and as purchaser of a part of the remaining rights of A. Hyatt Smith under the master’s sale in 1875.
This claim, we are satisfied, cannot and ought pot to prevail. In the first place, it is settled in the case that the dam was not built by the primary owners themselves- to a height ‘ sufficient to produce any greater head than four feet. It would be a fruitless waste of time to go over the vast amount of testimony on this point; it was conflicting, and the finding of the circuit court settles the question. The increase in the height of the dam and consequent increase of .head has been made at the expense of the grantees of the use of water and the owners of the reserved or “ Big Mill” water in proportionate shares. The amount'thus expended at various times exceeds $50,000. Time after •time has the dam been partially swept away by freshets, or worn out by ordinary wear and tear, and been rebuilt, made stronger, and improved by the owners of the water rights, and without help from the primary owners, save as they contributed their proportion as owners of the 3,200 square inches of reserved or “ Big Mill ” water. By reason of these expenditures so made, there now exists a substantial, solid dam, giving a permanent head of at least seven feet, in place of an unsubstantial affair pf brush, logs, and
*435The case shows that from beginning to end in the history of this power the owners of the sold water and the reserved water have invariably treated each other as the owners of the dam and all its power in proportionate shares according to the number of inches owned. They have bought, mortgaged, and sold on that basis; they have levied, collected, and expended assessments for repairs and rebuilding on that basis; they have always • used the water on that basis, each party claiming and using the number of inches to which he was entitled under whatever head the dam at *436the time afforded; they have entered into mutual, agreements for measuring, and paid ratable contributions to an engineer for regulating the use on that basis; they have, in connection with other owners of water-powers on Rock river at Beloit and Rockford, constructed a reservoir dam at or near Koshkonong, by means of which the flow of water is regulated and the ordinary flow increased in dry seasons.
It seems plain that the excess of power has been in fact created by the purchasers of water rights, and, if it were ■necessary, it would not seem to be very difficult to hold ■ that the primary owners and the appellants, who claim as grantees of the primary owners, are estopped at this period from claiming that this excess of power still belongs to them; but it is not necessary to invoke the principle of estoppel. When the primary owners had conveyed and reserved, in the aggregate, 13,532 square inches of water at a four-foot head, and exacted the covenants for repair and maintenance, they had undoubtedly conveyed the dam and the right to maintain it, because they had sold all the water the dam afforded, and compelled the grantees to maintain it. Smith v. Ford, 48 Wis. 115. Thereafter their only interest in the dam was as owners of the 3,200 inches of reserved water. And when, at a subsequent period, an owner of the perpetual right to use a definite quantity of water at a four-foot head, who was by virtue of such ownership, and of that alone, the owner of a proportionate share of the dam, deeded his rights to another, and exacted a covenant to maintain, we think it clear that he deeded the interest in the dam and power which he then had, whether he acquired that interest entirely by virtue of his original purchase or jointly by virtue of his purchase and his subsequent expenditures. We cannot divide the dam by a horizontal line at a point where it would furnish a head of four feet, and say that all above this line belongs to the primary *437owners. The inequitable character of such a ruling is too plain to require further comment.
This disposes of the points raised and discussed by the appellants.
Chief Justice Cole took part in the decision of this action, as well as in the decision of the case of Jackson Milling Co. v. Chandos, infra.
By the Court.— Judgment affirmed.
Oassoday and Pinney, JJ., took no part.