In 1891, Fisher received the first Ph.D. in economics granted by Yale. His faculty advisors were the theoretical physicist Willard Gibbs and the sociologist William Graham Sumner. As a student, Fisher had shown particular talent and inclination for mathematics, but he found that economics offered greater scope for his ambition and social concerns. His thesis, published by Yale in 1892 as "Mathematical Investigations in the Theory of Value and Prices", was a rigorous development of the theory of general equilibrium. When he began writing the thesis, Fisher had not been aware that Léon Walras and his continental European disciples had already covered similar ground. Nonetheless, Fisher's work was a very significant contribution and was immediately recognized and praised as first-rate by such European masters as Francis Edgeworth.