This lack of sympathy with the deeper currents of human progress reveals itself by many signs in almost all the phases of Frederick’s activity. In the art of war, indeed, he had witnessed too great an advance during his own career not to suppose that further advance was possible. He had himself given the infantry a mobility then unrivalled. He had introduced horse-artillery, and created the finest cavalry in the world. In his old age he turned to account the lessons of wars in both hemispheres, by raising his artillery to the importance of a separate arm and experimenting with the straggling tactics of the Americans. Literature and learning, however, he regarded with a less open mind. While Voltaire lived, he viewed him as the sole surviving man of letters. He treated the work of young Goethe, his own fervent admirer, with contempt and showed himself no less blind to the latent possibilities of natural science and mathematics. What he saw clearly was that these studies claimed much devotion, but sometimes failed to produce practical results. “Is it not true,” he demanded of d’Alembert, “that electricity and all the miracles that it reveals have only served to excite our curiosity? Is it not true that the forces of attraction and gravitation have only astonished our imagination? Is it not true that all the operations of chemistry are in the same case?” Euler himself had failed to make the fountains at Sans Souci play successfully, and the King jeered at geometricians as the very type of the pig-headed. In the campaign of 1778 an officer who trusted his theodolite in preference to his eye was bidden to go to the devil with his trigonometry. None of Frederick’s opinions or whims can be termed unimportant, for his power was so unfettered that he could embody any of them in acts of State. The building of the New Palace furnishes a hint of how great might have been the consequences had he given rein to a single enthusiasm in the sphere of art. But with this reservation it is in the domain of statecraft, especially in his system of foreign policy, his economic doctrine, and his theory of the organisation of the State, that we must seek the true measure of his mind.