Opinion by
Mr. Justice Elkin,In the view we take of this case it will not be necessary to consider in detail the many questions raised by the numerous assignments of error. We cannot accept as sound the contention of learned counsel for appellant that there was such clear, precise and indubitable evidence produced at the trial as to warrant a submission of the question of the reformation of the contract to the jury on the ground of fraud, accident or mistake. The presumption always is that a written instrument expresses the true intent of the parties who executed it, and when an attempt is made to vary the terms, set aside, or reform a contract solemnly entered into a heavy burden rests upon the party seeking the reformation. When an attempt is made to reform a contract in a common-law action the trial judge performs the functions of a chancellor, and if as a chancellor he would not reform a contract under the testimony offered, as a judge he should not permit a jury *649to do what he would not sanction in a proceeding in equity. These general rules are supported by ample authority: 24 Am. & Eng. Ency. of Law (2d ed.), 650; Stine v. Sherk, 1 W. & S. 195; Rowand v. Finney, 96 Pa. 192; Phillips v. Meily, 106 Pa. 536; Boyertown National Bank v. Hartman, 147 Pa. 558. In the case at bar the facts relied on by appellant are not sufficient to justify a chancellor in decreeing a reformation of the contract, and it necessarily follows that the learned court below committed no error in refusing to submit this question to the jury.
The lease of September 1, 1898, was executed between intelligent parties after several months of negotiations during which time all matters pertaining thereto were carefully considered, The conclusion is irresistible that the lease as executed is not only an expression of the intention of the parties, butis the definitely understood agreement entered into between them. If the lessor in the second lease had been an outside party, not interested in the first lease, it could not be successfully contended, in the absence of an express covenant to that effect, that a fault in the mine, or an unusual or unforeseen occurrence, or the quality of the coal in an adjoining property eould be set up to defeat a claim for the minimum royalty to be paid under the terms of the lease of the demised premises. Under the covenants of the second lease the lessee was bound to mine and take away from the 1,666-acre tract sufficient coal to produce a minimum royalty to the lessor of $3,200 per annum. This was a definite, absolute undertaking and could only be excused upon the conditions set out in the lease itself. Faults in the mine and other conditions relied on to excuse the payment of royalties in the second lease relate to the strata and the mining of coal underlying the therein described premises and have no reference to conditions which may have been found to exist on the adjoining property demised under the first lease. In these respects each lease must stand upon its own terms, the second is not dependent upon the first, nor is the first modified by the second. It is perfectly clear that it was the intention of the parties to the second lease to increase the output of coal on the one hand and to insure a larger amount of royalty on the other. The lessor desired to make his undeveloped lands productive; the lessee wanted to secure a larger *650tonnage of coal. The first lease executed in 1893 provided for the payment of royalty on at least 100,000 tons annually. It covered an area of 1,000 acres of land. The lessee acting with business prudence and foresight desired to control the output of the whole tract. With this end in view negotiations were opened between the parties which resulted in the execution of the second lease. It would do violence to the intelligence and integrity of the parties concerned to hold that after the second lease had been deliberately made and solemnly entered into the lessor would have no greater returns in royalty than he already enjoyed under the terms of the first lease, and yet this would be the practical result if the contention of appellant should prevail. One party to the contract was an eminent lawyer acting for himself and in his own interest, the other parties were reputable, prudent and capable business men. They were familiar with the property and understood the nature and character of the business about which they were contracting. They made their own covenants and are bound by them, one of which provides for the payment of a minimum royalty each year. A careful consideration of the able and exhaustive argument of learned counsel for appellant has failed to convince us that any facts were established at the trial that would excuse the payment of the minimum royalty provided to be paid in the second lease.
It may be conceded that there was some misunderstanding between the parties as to the location of shaft No. 2. In our opinion, the location of this shaft has nothing to do with the amount of coal to be mined or the minimum royalty to be paid under the covenants of said lease. Without regard to the location of this shaft, whether on the 1,666-acre tract or on the 1,000-acre tract, the minimum royalty must be paid according to the terms of the lease. If shaft No. 2 had been located within the boundaries of the 1,666-acre tract, the lessee would then be in position to set up faults in the mine, quality of the coal and other conditions relied on to excuse the payment of royalties, but inasmuch as the coal under this tract has not been touched, these questions cannot now be raised to defeat the claim for royalty due under the terms of the second lease. On the other hand, since the lessee thought proper to sink shaft No. 2 on the 1,000-acre tract and deemed this the better *651way of developing the property, conditions relating to that tract cannot be set up to defeat the claim for royalty due under the later lease. In these respects each lease is dependent upon and governed by conditions relating to the coal or the mining of the same within the boundaries described in the respective leases. The recent case of Troxell v. Anderson Coal Mining Company, 213 Pa. 475, applies with convincing force to the facts of the case at bar when as hereinbefore stated the first and second leases are treated as separate independent contracts.
The question as to the contribution of $8,000 to be made by the lessor toward the sinking of shaft No. 2 was properly submitted to the jury. It was a disputed question of fact and we do not see that any reversible error was committed by the learned trial judge in its submission. The twenty-second assignment seeks to convict the trial judge of error in refusing to compel the production of the private diaries of William Dorris, deceased, in the possession of an executrix, who was served with a duces tecum subpoena to produce them at the trial. We do not doubt that a diary may become an evidentiary writing, the production of which will be compelled in the trial of a cause under some circumstances and for proper purposes. It should be observed, however, that a diary is in the highest sense a personal and private record, not usually intended for public inspection, and when it is sought to invade this privacy by compelling the production of such a writing in evidence it is the duty of the trial judge to see that it is not done for the purpose of enabling one party to make undue inquisition into the private affairs of another; and the party making the offer must satisfy the court that it contains facts material or relevant to the issue. It has been held that an inspection of books and papers will be granted if facts and circumstances are shown which will warrant a presumption that the book or document sought contains evidence of the fact which the party applying has to establish: Lefferts v. Brampton, 24 How. Pr. 257. We do not question this rule, but it does not aid appellant in the case at bar, because no facts or circumstances were shown to warrant the presumption that the diary of William Dorris, deceased, contained any evidence of the facts sought to be established. Nor do we think it was the duty of the court, as *652contended by appellant, to require the production of the diaries, to have examined them, and, if found to contain entries relevant to the issue, to then admit them in evidence. This would have been a judicial fishing excursion which the court was not required to indulge, as a mere matter of discovery for the benefit of the party applying, without such party having first shown that the diaries contained facts pertinent to the issue involved.
In this connection it must not be overlooked that there was no definite allegation that the diaries contained evidence of the facts sought to be established, or that appellant had any knowledge of the contents of the diaries, nor were any facts or circumstances shown to the court by affidavit or otherwise that the diaries contained facts pertinent to the issue; and hence the cases cited from other jurisdictions and relied on by appellant are not applicable to the facts of the present ease. The learned court below in his opinion refusing a new trial clearly shows that appellant company did not bring itself within any rule which would require the production of the diaries. For these reasons no reversible error was committed in refusing to compel their production.
Assignments of error overruled and judgment affirmed.