the Commonwealth to act outside of the above explicitly enumerated areas is allowed by: 'the referral power': s51(xxxvii) allows State parliaments to refer matters they can legislate on to the Commonwealth. Section 51(xxxviii) allows state parliament(s) to refer to the Commonwealth Parliament any matter that the Parliament of the United Kingdom or the Federal Council of Australasia could legislate on their behalf at the establishment of the Commonwealth. 'the incidental power' s51(xxxix) allows the Commonwealth to act on matters 'incidental' to an enumerated head of power. Judicial interpretation The High Court of Australia has the jurisdiction to interpret the constitution. Many of the court's interpretations have focused on section 51, from cases arising out of disputes between the states and the Commonwealth Parliament. Core and incidental parts of s51 powers All heads of power in section 51 have an implied incidental area. The incidental area arises when the law operates on persons, Acts, or things outside the actual subject matter of the head of power. Valid laws in the incidental area will have an indirect, but sufficient connection to the head of power. Different judicial tests have arisen to test if the connection is sufficient. The dominant test is if the law in question is a reasonable and appropriate means of furthering an object or purpose in the power. Other tests are the 'reasonably necessary' test or 'reasonable fulfilment of the purpose'. Justice Mason preferred a 'proportionality' test that took into account the adverse effects of incidental laws. Tied grants Section 51 appears to limit the areas of federal involvement. However, under section 96 of the Australian Constitution the Commonwealth Parliament has the power to grant money to any State, "on such terms and conditions as the Parliament thinks fit." In effect, the Commonwealth can make grants subject to States implementing particular policies in their fields of legislative responsibility. Such grants, known as tied grants (since they are tied to a particular purpose), have been used to give the federal parliament influence over state policy matters such as public hospitals and schools. Section 96 does not compel a state to accept a grant, so constitutionally a state may refuse a grant and not implement any policy conditions. However, since a uniform federal system of income tax was introduced in 1942 (under s51(ii)) a vertical fiscal imbalance has arisen and the Commonwealth Parliament has had a vastly larger budget. It also