It is familiar law that a state has no power to tax the property of the United States within its limits. This exemption of their property from state taxation—and by state taxation we mean any taxation by authority of the state, whether it be strictly for state purposes or for mere local and special objects—is founded upon that principle which inheres in every independent government, that it must be free from any such interference of another government as may tend to destroy its powers or impair their efficiency. If the property of the United States could be subjected to taxation by the state, the object and extent of the taxation would be subject to the state's discretion. It might extend to buildings and other property essential to the discharge of the ordinary business of the national government, and in the enforcement of the tax those buildings might be taken from the possession and use of the United States. The constitution vests in congress the power 'to dispose of and make all needful rules and regulations respecting the territory or other property belonging to the United States.' And this implies an exclusion of all other authority over the property which could interfere with this right or obstruct its exercise. Van Brocklin v. State, 117 U. S. 151, 168, 6 Sup. Ct. Rep. 670. This doctrine of exemption from taxation of the property of the United States, so far as lands are concerned, is in express terms affirmed in the constitution of Wisconsin, which ordains that the state 'shall never interfere with the primary disposal of the soil within the same by the United States, nor with any regulations congress may find necessary for securing the title in such soil to bona fide purchasers thereof, and no tax shall be imposed on land the property of the United States.' Const. 1848, art. 2, § 2.

It follows that all the public domain of the United States within the state of Wisconsin was in 1883 exempt from state taxation. Usually the possession of the legal title by the government determines both the fact and the right of ownership. There is, however, an exception to this doctrine with respect to the public domain, which is as well settled as the doctrine itself; and that is, that where congress has prescribed the conditions upon which portions of that domain may be alienated, and provided that upon the performance of the conditions a patent of the United States shall issue to the donee or purchaser, and all such conditions are complied with, the land alienated being distinctly defined, it only remaining for the government to issue its patent, and until such issue holding the legal title in trust for him, who in the mean time is not excluded from the use of the property,—in other words, when the government has ceased to hold any such right or interest in the property as to justify it in withholding a patent from the donee or purchaser, and it does not exclude him from the use of the property,—then the donee or purchaser will be treated as the beneficial owner of the land, and the same be held subject to taxation as his property. This xception to the general doctrine is founded upon the principle that he who has the right to property, and is not excluded from its enjoyment, shall not be permitted to use the legal title of the government to avoid his just share of state taxation. Thus in Carroll v. Safford, 3 How. 441, 460, the complainant had entered certain lands belonging to the United States, in the local land-office, paid for them the required price, and received from the office a land certificate. Patents were issued for them, but, before their issue, the lands were assessed for taxation and sold for the taxes. The question whether they were subject to taxtion by the state after their entry, and before the patents were issued, was answered in the affirmative. Said the court: 'When the land was purchased and paid for, it was no longer the property of the United States, but of the purchaser. He held for it a final certificate, which could no more be canceled by the United States than a patent.' And again: 'It is said the fee is not in the purchaser, but in the United States, until the patent shall be issued. This is so, technically, at law, but not in equity. The land in the hands of the purchaser is real estate, descends to his heirs, and does not go to his executors or administrators.' And again: 'Lands which have been sold by the United States can in no sense be called the property of the United States. They are no more the property of the United States than lands patented. So far as the rights of the purchaser are considered, they are protected under the patent certificate as fully as under the patent. Suppose the officers of the government had sold a tract of land, received the purchase money, and issued a patent certificate. Can it be contended that they could sell it again, and convey a good title? They could no more do this than they could sell land a second time which had been previously patented. When sold, the government, until the patent shall issue, holds the mere legal title for the land in trust for the purchaser; and any second purchaser would take the land charged with the trust.' In Witherspoon v Duncan, 4 Wall. 210, 218, a similar question arose, and was in like manner answered. Said the court: 'In no just sense can lands be said to be public lands after they have been entered at the land-office, and a certificate of entry obtained. If public lands before the entry, after it they are private property. If subject to sale, the government has no power to revoke the entry and withhold the patent. A second sale, if the first was authorized by law, confers no right on the buyer, and is a void act.' And again: 'The contract of purchase is complete when the certificate of entry is executed and delivered, and thereafter the land ceases to be a part of the public domain. The government agrees to make proper conveyance as soon as it can, and in the mean time holds the naked legal fee in trust for the purchaser, who has the equitable title.' See, also, Railway Co. v. Prescott, 16 Wall. 603, 608; Railway Co. v. McShane, 22 Wall. 444, 461.

In the light of these decisions, it will be necessary, in order to determine the liability of the property held by the plaintiff to taxation in 1883, to consider the nature and extent of its interest in the property at that time acquired under the grant of congress of May, 1864, and by its subsequent construction of the road. Numerous grants of land were made by congress between 1860 and 1880, to aid in the construction of railroads,—some directly to incorporated companies, others to different states; the lands to be by them transferred to companies by whom the construction of the roads might be undertaken. The different acts making these grants were similar in their general provisions, and so many of them have been, at different times, before this court for consideration that little can be said of their purport and meaning, the title they transfer, and the conditions upon which the lands could be used and disposed of, which has not al eady and repeatedly been said in its decisions. Each grant gave a specified quantity of lands, designated by sections along the route of the proposed road, with the exception of such as might, when the line of the road should be definitely fixed, have been disposed of or reserved by the government, or to which a pre-emption or homestead right might then have attached. For these excepted sections, which otherwise would have been taken from those designated along the line of the road, other lands beyond those sections within a specified distance were allowed to be selected. The title conferred was a present one, so as to insure the donation for the construction of the road proposed against any revocation by congress, except for non-performance of the work within the period designated, accompanied, however, with such restrictions upon the use and disposal of the lands as to prevent their diversion from the purposes of the grant. It was the practice of the land department, as shown by the evidence in this record, up to the decision of Leaven worth, etc., R. Co. v. U. S., 92 U. S. 733, (in April, 1876,) to allow deficiencies in the quantity of land intended to be granted, arising from sales or other disposition made before the date of the grant, as well as those made subsequently, and those arising from the attachment of preemption or homestead rights, to be supplied from lands lying beyond the original sections, within what were termed the 'indemnity limits.' This practice was held in Railroad Co. v. Barney, 113 U. S. 618, 625, 5 Sup. Ct. Rep. 606, to have been correct. As the court there said: 'The policy of the government was to keep the public lands open at all times to sale and pre-emption, and thus encourage the settlement of the country, and, at the same time, to advance such settlement by liberal donations to aid in the construction of railways. The acts of congress, in effect, said: 'We give to the state certain lands to aid in the construction of railways lying along their respective routes, provided they are not already disposed of, or the rights of settlers under the laws of the United States have not already attached to them, or they may not be disposed of or such rights may not have attached when the routes are finally determined. If at that time it be found that of the lands designated any have been disposed of, or rights of settlers have attached to them, other equivalent lands may be selected in their place, within certain prescribed limits.' The encouragement to settlement by aid for the construction of railways was not intended to interfere with the policy of encouraging such settlement by sales of the land, or the grant of pre-emption rights.' The court accordingly held that the indemnity clause covered losses from the grant by reason of sales and the attachment of pre-emption rights previous to the date of the act, as well as by reason of sales and the attachment of pre-emption rights between that date and the final determination of the route of the road.

After the decision of the court in the Leavenworth Case, the land department changed its practice, and refused to allow the deficiencies, arising from sales or other disposition made, or from the attachment of pre-emption or homestead rights before the date of the act to be made up from selections within the indemnity limits. But that decision did not warrant the change. The question in that case was not, for what deficiencies indemnity could be had, but what lands could be taken for deficiencies which existed? If what was then said indicated that deficiencies which could be supplied were limited to such as might arise after the passage of the act, it was a mere dictum, not essential to the decision, and therefore not authoritative and binding. The refusal of the land department, therefore, to allow the deficiencies arising in the sections within the place limits in this case to be supplied by selections from the indemnity lands, and to issue patents of the United States for th m, was erroneous.

The question now arises as to how far this refusal affected the legal or equitable title of the company to the lands taxed in 1883, for which it only obtained a patent in 1884. The lands taxed amounted to 11 parcels of 40 acres each, lying within the original sections named in the grant,—that is, within the 10-miles limit from the line of the road,—and the remainder were within the indemnity limits. Neither were allowed, because, by excluding the deficiencies arising before the date of the grant from indemnity, the whole amount of the lands granted had already been patented. So far as the 11 parcels of 40 acres each are concerned, the right of the plaintiff to them, and to a patent for them, had, as early as 1877, become complete under the terms of the granting act. The line of the railroad had been definitely fixed on the 7th of October, 1869; and the 3 20-mile sections, Nos. 5, 6, and 7, were all completed in June, 1877, and supplied with the buildings and appurtenances specified in the act to entitle the company to a patent for them from the United States. The title conferred by the grant was necessarily an imperfect one, because, until the lands were identified by the definite location of the road, it could not be known what specific lands would be embraced in the sections named. The grant was, therefore, until such location, a float. But when the route of the road was definitely fixed, the sections granted became susceptible of identification, and the title attached to them and took effect as of the date of the grant, so as to cut off all intervening claims. Schulenberg v. Harriman, 21 Wall. 44, 60; Leavenworth etc., R. Co. v. U. S., 92 U. S. 733, 741; Missouri, etc., R. Co. v. Kansas Pac. Ry. Co., 97 U. S. 491, 496; Railway Co. v. Baldwin, 103 U. S. 426, 429. The road having been built as early as June, 1887, and supplied, as required, with the appurtenances specified, the company was entitled to have the restrictions upon the use of the land released. It had then, to the 11 40-acre parcels which were capable of identification, an indefeasible right or title; it matters not which term be used. The subsequent issue of the patents by the United States was not essential to the right of the company to those parcels, although in many respects they would have been of great service to it. They would have served to identify the lands as coterminous with the road completed; they would have been evidence that the grantee had complied with the conditions of the grant, and to that extent that the grant was relieved of possibility of forfeiture for breach of them; they would have obviated the necessity of any other evidence of the grantee's right to the lands; and they would have been evidence that the lands were subject to the disposal of the railroad company, with the consent of the government. They would have been in these respects deeds of further assurance of the patentee's title, and therefore a source of quiet and peace to it in its possessions.

There are many instances in the Reports where such effect as is here stated has been given to patents authorized or directed to be issued to parties, notwithstanding they had previously received a legislative grant of the premises, or their title had been already confirmed. In Langdeau v. Hanes, 21 Wall. 521, 529, we have one of that kind. There this court said: 'In the legislation of congress a patent has a double operation. It is a conveyance by the government, when the government has any interest to convey; but, where it is issued upon the confirmation of a claim of a previously existing title, it is documentary evidence, having the dignity of a record, of the existence of that title, or of such equities respecting the claim as justify its recognition and confirmation. The instrument is not the less efficacious as evidence of previously existing rights, because it also embodies words of release or transfer from the government.' We are of opinion, therefore, that these 11 40-acre parcels were in 1883 subjec to taxation by the state of Wisconsin. The lands had become the property of the railroad company, and there was nothing to hinder their use and enjoyment. For that purpose it is immaterial whether it be held that the company then had a legal and indefeasible title to the lands, or merely an equitable title to them, to be subsequently perfected by patents from the government.

But as to the remainder of the lands taxed, which fell within the indemnity limits, the case is different. For such lands no title could pass to the company, not only until the selections were made by the agents of the state appointed by the governor, but until such selections were approved by the secretary of the interior. The agent of the state made the selections, and they had been properly authenticated and forwarded to the secretary of the interior. But that officer never approved of them. Nor can such approval be inferred from his not formally rejecting them. He refused, as already stated, to issue to the company any patents for any more lands, insisting that it had already received over 40,000 acres too much, and he directed the commissioner of the general land-office to require the company to restore this excess to the government. The approval of the secretary was essential to the efficacy of the selections, and to give to the company any title to the lands selected. His action in that matter was not ministerial, but judicial. He was required to determine, in the first place, whether there were any deficiencies in the land granted to the company which were to be supplied from indemnity lands; and, in the second place, whether the particular indemnity lands selected could be properly taken for those deficiencies. In order to reach a proper conclusion on these two questions, he had also to inquire and determine whether any lands in the place limits had been previously disposed of by the government, or whether any pre-emption or homestead rights had attached before the line of the road was definitely fixed. There could be no indemnity unless a loss was established. And, in determining whether a particular selection could be taken as indemnity for the losses sustained, he was obliged to inquire into the condition of those indemnity lands, and determine whether or not any portion of them had been appropriated for any other purpose, and, if so, what portion had been thus appropriated, and what portion still remained. This action of the secretary was required, not merely as supervisory of the action of the agent of the state, but for the protection of the United States against an improper appropriation of their lands. Until the selections were approved there were no selections in fact, only preliminary proceedings taken for that purpose, and the indemnity lands remained unaffected in their title. Until then, the lands which might be taken as indemnity were incapable of identification; the proposed selections remained the property of the United States. The government was, indeed, under a promise to give the company indemnity lands in lieu of what might be lost by the causes mentioned. But such promise passed no title, and, until it was executed, created no legal interest which could be enforced in the courts. The doctrine that until selection made no title vests in any indemnity lands, has been recognized in several decisions of this court. Thus in Ryan v. Railroad Co., 99 U. S., 382, 386, in considering a grant of land by congress, in aid of the construction of a railroad, similar in its general features to the one in this case, the court said: 'Under this statute, when the road was located and the maps were made, the right of the company to the odd sections first named became ipso facto fixed and absolute. With respect to the 'lieu lands,' as they are called, the right was only a float, and attached to no specific tracts until the selection was actually made in the manner prescribed.' And again, speaking of a deficiency in the land granted, it said: 'It was within the secondary or indemnity territory where that deficiency was to be supplied. The railroad company had not and could not have any claim to it until specially selected, as it was, for that purpose.' The selection had been approved by the secretary. In St. Paul R. Co. v. Winona R. Co., 112 U. S. 720, 731, 5 Sup. Ct. Rep. 334, the court, speaking of a previous decision, said: 'The reason of this is that, as no vested right can attach to the lands in place (the odd-numbered sections within six miles of each side of the road) until these sections are ascertained and identified by a legal location of the line of the road, so, in regard to the lands to be selected within a still larger limit, their identification cannot be known until the selection is made. It may be a long time after the line of the road is located before it is ascertained how many sections, or parts of sections, within the primary limits, have been lost by sale or pre-emption. It may be still longer before a selection is made to supply this loss.' In Sioux City R. Co. v. Chicago Ry. Co., 117 U.S. 406, 408, 6 Sup. Ct. Rep. 790, where the railroad grant as to indemnity lands was substantially similar to the one in this case, and one of the questions was as to the title to the indemnity lands, the court said: 'No title to indemnity lands was vested until a selection was made by which they were pointed out and ascertained, and the selection made approved by the secretary of the interior.' In Barney v. Railroad Co., 117 U. S. 228, 232, 6 Sup. Ct. Rep. 654, the court said: 'In the construction of land-grant acts in aid of railroads, there is a well-established distinction observed between 'granted lands' and 'indemnity lands.' The former are those falling within the limits specially designated, and the title to which attaches when the lands are located by an approved and accepted survey of the line of the road filed in the land department, as of the date of the act of congress. The latter are those lands selected in lieu of parcels lost by previous disposition or reservation for other purposes, and the title to which accrues only from the time of their selection.' The same view has been held by different attorney generals of the United States, in their official communications to heads of the departments, where selections of the public lands have been granted, subject to the approval of the secretary of the interior, (Cape Mendocino Light-House Site, 14 Ops. Atty. Gen. 50; Portage Land Grant, Id. 645,) and such has been the consistent practice of the land department. The uniform language is that no title to indemnity lands becomes vested in any company or in the state until the selections are made; and they are not considered as made until they have been approved, as provided by statute, by the secretary of the interior. It follows from these views that the indemnity lands described in the complaint were not subject to taxation as the property of the railroad company in 1883. The judgment of the supreme court of Wisconsin must therefore be reversed, and the cause remanded, with directions to enter a decree perpetually enjoining the collection of the taxes levied in the year 1883 upon the indemnity lands, and dismissing the complaint as to the 11 parcels, of 40 acres each. And it is so ordered.