Opinion by
Mb. Justice Mitchell,The third clause of the agreement between the city of Pitts-burg and the appellant, provides that the appellant shall make its assessments of water rents in the stipulated territory “ at rates not higher than those in each class of water rents assessed by the city of Pittsburg in the wards between the rivers.” This is the clause on which the bill is founded, and if it were all that the agreement contained on the subject it might fairly be held to apply to exemptions, although it speaks only of “assessments” and “rates” for different classes of rents, and does not in terms refer to exemptions at all. The next clause however provides that the city shall furnish water to her own mains then laid or being laid, for the purpose of supplying the fire-plugs and watering the streets along the lines of said mains. The next, or fifth clause, then provides that the appellant shall supply all the other fire-plugs then or thereafter put in by the city, without any charge. These two clauses show conclusively that the subject of exemptions was considered and provided for by the parties. If the construction contended for by the complainants is correct then the city, making no assessment for its own fire-plugs or street watering between the rivers, as it is agreed that it did not then or now, would have been entitled to have all its plugs on the south side supplied by the water company free, and clause five would have been superfluous, and clause four in conflict with the intent of the parties. These two clauses therefore show the construction put by the parties themselves on the contract, and they show also that the subject of exemptions was in their minds and was disposed of by them. The specification of a limited class of exemptions, fire-plugs not on the line of the city’s pipes already laid or being laid, shows that no other class was to be exempt. Expressio unius exclusio alterius.
This inevitable deduction from the language of the agreement is strengthened, though it is not necessary, by the circumstances. The water company was then charging sehoolhouses. If the intention was that thereafter it should not do so, it is to be presumed that their exemption would have been provided for as that of fire-plugs was. And the conduct of the parties is in entire accord with this view, for the water rents were regularly charged by the appellant and regularly paid by the *86school districts for eight years, before the latter gave any sign of their present idea of their rights. Even if the contract were much more obscure or doubtful than it is, this conduct of the parties for such a period would have great weight in a court of equity against the present claim.
As to the suggestion that the city may place a nominal assessment on its schoolhouses, and the water company being obliged to follow, there would result a superficial and unsubstantial distinction between being bound by a nominal assessment and not bound by an exemption, it is only necessary to say that if the city should by such a subterfuge attempt to do indirectly what it has no power to do directly, a court of equity would have no difficulty in dealing promptly and effectually with such an effort.
Decree reversed, and bill directed to be dismissed with costs.