delivered the opinion of the Court.
This controversy rises from a petition filed by Jack C. Robinson, doing business as Robinson Freight Lines, before the Railroad & Public Utilities Commission, to secure certificates of convenience and necessity to license freight haulage over 8 routes of public highways in Tennessee. The petition was resisted by all common carriers already having certificates of convenience and necessity, covering the routes specified in Robinson’s petition. We will refer herein to the Robinson Freight Lines as “Robinson,” and to those opposing his petition as “the Hoover Group.” After a full hearing and the introduction of evidence, the Commission found that “the public convenience and necessity will be promoted by the creation of the proposed service,” and granted the petition of Robinson for certificates over the 8 routes.
Thereupon carriers in the Hoover Group filed petitions for certiorari in the Chancery Court of Davidson County, *598and the writs being granted, the case came on to he heard, before the Chancellor.
The first and principal question was the effect of Chapter 261, Public Acts of 1951, effective March 16, 1951, by which Code Section 9014 was amended to provide “In making such findings of fact the Chancellor shall weigh the evidence and determine the facts -by the preponderance of the proof.” Since the proceeding before the Utilities Commission had been held before the effective date of the Act, though the effective date of the Act was prior to the hearing in the Chancery Court, the Chancellor held that the Act did not apply, and proceeded to consider the writ under the usual procedure for a common law writ of certiorari as such proceeding was regular prior to the amendment of 1951. Robinson’s original petition before the Utilities Commission sought certificates of convenience and necessity over 8 routes. The Chancellor found that there was no evidence whatever to support the issuance of certificates over 5 of these routes, but that there was material, substantial evidence to support the issuance over the remaining 3 routes. He, therefore, concluded that the action of the Commission as to the 5 routes not supported by evidence was arbitrary and illegal, but affirmed the issuance of the other 3 certificates.
No appeal was perfected from the action of the Chancellor in annulling* the certificates over the 5 routes not supported by evidence, and his action in that regard has become final. As to the other 3 routes, the Hoover Group perfected its appeal to the Court of Appeals, and in substance, that Court held: (1) That the amendment of 1951 being in effect at the time of the hearing- in Chancery Court, and being procedural merely, should have guided the Chancellor in his disposition of the case; (2) That though there was material substantial evidence to sup*599port the finding of the Commission as to the 3 routes in controversy, that the evidence strongly “preponderated” against the finding of the Commission that public convenience and necessity would be promoted by issuing certificates to Robinson over those routes; and (3) Modified the decree of the Chancellor, and cancelled in its entirety the order of the Commission granting certificates to Robinson, and dismissed his petition.
Robinson has filed petition for certiorari in this Court, which, after filing a memorandum, we denied, but on. petition to rehear, when it developed that a constitutional question was involved, we granted the writ, have heard argument and the case is so before us for disposition.
As this Court has repeatedly held, the review before the Chancellor on the writ of certiorari was limited to the review provided by the common law writ, although in strictness no common law writ now exists in Tennessee, and the writ here was that defined by Code-Section 8989. Dunlap v. Dixie Greyhound Lines, 178 Tenn. 532, 160 S. W. (2d) 413; Tenn. Cartage Co., Inc., v. Pharr, 184 Tenn. 414, 199 S. W. (2d) 119; Hoover Motor Express Co., Inc., v. Taylor, 185 Tenn. 88, 203 S. W. (2d) 366. By Code Section 8989, review is limited to a determination whether the “inferior tribunal, board, or officer exercising judicial functions has exceeded the jurisdiction conferred, or is acting illegally”.
“The next contention is that petitioner has the right to have the writ of certiorari to the end that he may have the matter heard or retried upon the merits. * * * The answer to this is that it is only where the writ of certiorari lies as a substitute for an appeal or a writ of error, or, possibly, instead of audita querela, that the writ will operate to give to the petitioner a new trial upon the merits.” (Lur-*600ton, J.) Tomlinson v. Board of Equalization, 88 Tenn. 1, 11, 12 S. W. 414, 416, 6 L. R. A. 207.
In a number of cases, for example, Savage Co. v. City of Knoxville, 167 Tenn. 642, 72 S. W. (2d) 1057; Anderson v. City of Memphis, 167 Tenn. 648, 72 S. W. (2d) 1059; McKee v. Board of Elections, 173 Tenn. 269, 276, 117 S. W. (2d) 752, this Court lias expressly lield that the distinction between the common law writ of certiorari, Code Section 8989, and the statutory writ in lieu of appeal, Code Section 8990, was not destroyed by the enactment of Code Sections 9008-9018, ,and that those sections did not operate to enlarge the scope of review permissible to the judicial branch of the Government under the common law writ of certiorari. In defining the effect of these Code Sections, Judge Green said:
“Section 9008 of the Code neither enlarges nor diminishes the scope of review by certiorari. It only prescribes procedure. Anderson v. [City of] Memphis, 167 Tenn. 648, 72 S. W. (2d) 1059 ; Prosterman v. [Tennessee State] Board of Dental Examiners, 168 Tenn. 16, 73 S. W. (2d) 687.” McKee v. Board of Elections, 173 Tenn. 269, 274, 117 S. W. (2d) 752, 754.
Code Section 9008 affords relief only if the inferior board or commission is or has .acted c ‘ arbitrarily, fraudulently, or illegally”. Richardson v. Reese, 165 Tenn. 661, 57 S. W. (2d) 797, 800.
“ ‘Certiorari’ at common law performed the function of aid to a review and supervision of the proceeding’s of inferior boards and tribunals by a superior tribunal, not taking the place of appeal or writ of error, but bringing up the entire record in order to a determination whether there had been an absence or excess of jurisdiction, or a failure to *601proceed according to the essential requirements of the law.” Conners v. City of Knoxville, 136 Tenn. 428, 432, 189 S. W. 870, 871.
“Applicable to the common-law writ is this excerpt:
“ ‘It must be borne in mind that the functions of certiorari are simply to ascertain the validity of proceedings before a court of justice, either on the charge of their invalidity, because the essential forms of the law have not been observed, or on that of the want of jurisdiction in the court entertaining them. The writ has never been employed to inquire into the correctness of the judgment rendered where the court had jurisdiction, and was therefore competent. Hence it has been held that the supervisory jurisdiction of the court on a certiorari must be restricted to an examination into the external validity of the proceedings had in the lower court. It cannot be exercised to review the judgment as to its intrinsic correctness, either on the law or on the facts of the case. The supervisory powers of the court should not be confounded with its appellate jurisdiction.’ 5 R.C.L., 251; State [ex rel. Matranga] v. Judge, 42 La. Ann. 1089, 8 So. 277, 10 L. R. A. 248.” State ex rel. McMorrough v. Hunt, 137 Tenn. 243, 250-251, 192 S. W. 931, 933.
By its unanimous opinion In re Cumberland Power Co., 147 Tenn. 504, 249 S. W. 818, this Court expressly held unconstitutional Chapter 107, Public Acts of 1921, by which the Legislature undertook to give a right of appeal to this Court from the Railroad & Public Utilities Commission.
If, as did the Court of Appeals, Chapter 261, Public Acts of 1951, supra, is to be construed as imposing on *602the Chancellor a hearing on appeal, or on a certiorari in lien of appeal, such construction would render the Act unconstitutional for the reasons stated in the opinion In re Cumberland Power Co., supra. By its opinion, the Court of Appeals has undertaken to perform an administrative or legislative function, which is beyond its competency.
Sec. 1, of art. II, of the Constitution of 1870, divides the Grovernment into three distinct and independent departments, and Sec. 2, of art. II, forbids the exercise by one of the function of another department. Definition of the exact limitation of the function of each of the three departments is not undertaken in the Constitution. That definition, as a matter of construction and interpretation of the Constitution, is the highest function of the Judiciary whose construction prevails over any construction or interpretation of the Constitution undertaken either by the Legislature or the Executive.
“This principle is wholly and exclusively American. It is America’s original contribution to the science of law.” Beveiidge, “The Life of John Marshall,” Yol. Ill, p. 142.
“If Congress remains at liberty to give this court appellate jurisdiction, where the constitution has declared their jurisdiction shall be original; and original jurisdiction where the constitution has declared it shall be appellate; the distribution of jurisdiction, made in the constitution, is form without substance.” Marbury v. Madison, 1 Cranch, U. S., 137, 2 L. Ed. 60, 72. Cooley, Constitutional Limitations, Vol. 1, 8th ed., Chapter 7, et aliunde.
This Court has frequently declared its adoption of the principle expounded in Marbury v. Madison, supra, and *603lias declared that its interpretation of the State Constitution is controlling.
“But it is the glory ,and the boast of our written constitution, that the powers of the law-makers are restricted and defined; and while it is the legitimate and lawful province of the Supreme Judicial Tribunal of the Union to determine the validity of a statute assumed to have been enacted under the authority of the organic law, it is no less the prerogative of the State tribunal to interpret its own State laws, and to pronounce upon their compatibility with the supreme organic law.” Lonas v. State, 50 Tenn. 287, 301-302. Huntsman’s Lessee v. Randolph, 6 Tenn. 263, 271; Nelson v. Allen, 9 Tenn. 3601, 379; Wright v. Cunningham,, 115 Tenn. 445, 91 S. W. 293; Governor v. Porter, 24 Tenn. 165; Fisher’s Negroes v. Dabbs, 14 Tenn. 119.
This Court has expressly held that the Railroad & Public Utilities Commission is not a Court, In re Cumberland Power Co., supra, that it performs administrative and legislative functions, Nashville, C. & St. L. RR. v. Browning, 176 Tenn. 245, 140 S. W. (2d) 781, and any different construction by the Legislature of statutes under which the Railroad & Public Utilities Commission operates, would be a nullity and void, since the construction of Sections 1 and 2 of art. II, of the Constitution is exclusively a judicial function. Fisher’s Negroes v. Dabbs, 14 Tenn. 119; Governor v. Porter, 24 Tenn. 165, 167-168; Arrington v. Cotton, 60 Tenn. 316, 319; Erwin v. State, 116 Tenn. 71, 96, 93 S. W. 73.
“Prom the foregoing it is apparent that the broad •general purpose of the acts in question is to confer upon the Railroad and Public Utilities Commission powers and functions which are primarily legislative *604and executive, and that the power to hear and determine controversies, the quasi-judicial power, is merely incidental thereto. The proposition that the Legislature intended or attempted to create a court by the acts above referred to and to vest it with the power to make rules, interpret and execute them, cannot be 'successfully maintained. The Railroad and Public Utilities Commission is authorized to initiate and prosecute its own proceedings before itself; and such proceedings are to be heard, decided, and its determination therein is authorized to be enforced by itself. A tribunal exercising such commingled legislative, executive, and judicial functions, from its very nature cannot be made a court.” In re Cumberland Power Co., supra, 147 Tenn. at page 515, 249 S. W. at page 821.
Code Sections 9008-9018, without prior legislative sanction, were enacted as a part of the Code of 1932. So far as their language shows, these sections apply both to the procedure under petitions for the common law writ of certiorari, Code Sec. 8989, and the statutoiy writ of certiorari, Code Sec. 8990. Chapter 261, Public Acts of 1951, amends Code Sec. 9014 without undertaking to distinguish the effect it may have on the procedure under the common law writ, from that under the statutory writ. For the determination of the present controversy and decision of this case, it is only necessary for us to determine the effect the amendment had on procedure under the common law writ of certiorari. As we have stated above, the common law writ does not bring up for determination, .any question except the question whether the inferior board or tribunal (1) has exceeded its jurisdiction, or (2) has acted illegally, arbitrarily or fraudulently. The effect of the amendatory Act was, therefore, *605only to require the Chancellor to review the evidence which had been introduced before the Commission, and to determine by a preponderance of the evidence, whether the Commission had' acted beyond its jurisdiction, arbitrarily, fraudulently or illegally. Since this was the long established limit of appropriate judicial review under the common law writ, the amendatory Act of 1951 could have no further or greater effect on procedure under the common law writ, whatever may be the effect of the amendment on a proceeding under the statutory writ, Code Sec. 8990.
In the present case, the decision whether certificates of convenience and necessity shall be issued for the use of State highways for hauling freight by a motor carrier, is clearly an administrative function of government. Control and regulation of certain motor carriers were vested in the Railroad and Public Utilities Commission by the Motor Carriers Act, Chapter 119, Public Acts of 1933, Code Supplement, 5501.1-5501.23. By the Act, the Utilities Commission is given the same control over certain motor carriers as it had had theretofore over so-called “utilities” or “corporations affected with a public interest.” The Act expressly so provides, Code Supplement, Secs. 5501.15-5501.16. That control is exclusive and final. McCollum v. Southern Bell T. & T. Co., 163 Tenn. 277, 280, 43 S. W. (2d) 390. The action of the Commission in giving or withholding certificates of convenience and necessity is an administrative function no different from the action of the Commission in the rate-making power of which Judge Cook, speaking for a unanimous Court, said:
“The courts cannot directly or indirectly exercise the rate-making power * * *.” Lewis v. Nashville Gas Co., 162 Tenn. 268, 283, 40 S. W. (2d) 409, 414.
*606‘ ‘ * * * ‘ That neither the legislative nor the executive branches can constitutionally assign to the judicial any duties hut such as are properly judicial, and to be performed in a judicial manner. ’ ” Muskrat v. U. S., 219 U. S, 346, 348, 31 S. Ct. 250, 252, 55 L. Ed. 246, 248; Hayburn’s Case, 2 Dall., U. S., 409, 1 L. Ed. 436.
Under the common law writ of certiorari, questions of law only will be reviewed by the Courts. The Law of Certiorari by George E. Harris, Sec. 48, Sec. 59, Sec. 82; 42 Am. Jur., Public Administrative Law, p. 622, Sec. 210. An order of the Commission which is not supported by any evidence is arbitrary and void, and therefore, within judicial power to quash under the common law writ of certiorari. 42 Am. Jur., Public Administrative Law, Sec. 150, p. 496. The question whether there is any material evidence to support the finding and order of the Commission is, therefore, a matter of law for the Court upon review, and to ascertain that, whether there is any material evidence, is the limited purpose for which the evidence introduced before the Commission is admissible in the Court granting the writ of common law certiorari. Harris, Certiorari, supra; Alton R. Co. v. U. S., 315 U. S. 15, 62 S. Ct. 432, 86 L. Ed. 586; U. S. v. Morgan, 313 U. S. 409, 61 S. Ct. 999, 85 L. Ed. 1429; Interstate Commerce Commission v. Louisville & N. R. Co., 227 U. S. 88, 33 S. Ct. 185, 57 L. Ed. 431.
Under Code Sec. 9014, it is provided that additional evidence may be introduced in the Court granting the writ of certiorari, but on the hearing on the common law writ, that evidence is limited to the question presented, namely, whether the Board or Commission has exceeded its jurisdiction or acted fraudulently, illegally or arbitrarily.
*607“Under this provision, if the petition be for the common-law writ of certiorari, its averments of illegal action or usurpation of authority by the commission or board may be supported or refuted by additional evidence; and if the writ granted be the statutory writ, in lieu of appeal, the hearing is de novo, and either party is free to support his contentions by evidence bearing on the issues presented.” Anderson v. City of Memphis, 167 Tenn. 648, 653, 72 S. W. (2d) 1059, 1060.
Since the Tennessee statutes creating the Public Utilities Commission were modeled on the Federal statutes, Federal decisions are particularly persuasive in resolving questions arising under those statutes. Oman v. Tennessee Cent. Ry. Co., 7 Tenn. App. 141; Cleveland C., C. & St. L. R. Co. v. Southern Coal & Coke Co., 147 Tenn. 433, 441, 248 S. W. 297.
The weight to he given particular evidence is a matter peculiarly within the province of the trier of the facts, unhampered by mechanical rules governing the weight or effect of evidence. 42 Am. Jur., Public Administrative Law, Sec. 132, p. 467.
"To consider the weight of the evidence is beyond our province.” (Brandeis, J.) Western Papermakers Chemical Co. v. U. S. of America, 271 U. S. 268, 46 S. Ct. 500, 501, 70 L. Ed. 941, 943.
The judgment of the Court of Appeals is reversed, and with the foregoing explanation, the decree of the Chancellor is affirmed at the cost of the respondents.
TomliNsoN, Justice, dissents.