One powerful method of investigation in Vico's hands is the comparative method, consisting in the comparison of better-known processes of development with those known imperfectly or in parts only, and the consequent reconstruction of the latter on the basis of the former. So for instance the principle of heroism, revealed by evidence found in Roman history, helps to explain the legendary history of the Greeks, to supply the deficiencies of that of Egypt and to shed light on the unknown history of all other nations of antiquity. Without denying the fact of transmission from one nation to another, Vico poured scorn upon the abuse of this conception, and minimised its value in the case of primitive societies: using in its place the idea of spontaneous development and endeavouring to reconstruct the process by the comparative method. But he took this method in a very broad sense, and made use in it of materials drawn from the most widely varying countries and periods. To explain for example how the thundering sky suggested to primitive man the idea of a god, he mentions the fact that the natives of America, when first they heard the noise and recognised the deadly effects of firearms in the hands of the Spaniards, believed them to be gods: the rhapsodists of the Homeric poems reminded him of the singers on the quay at Naples with their ballads of Roland and the paladins: the transformations or metamorphoses described by the ancient poets resembled the tales of goblins and fairies still told by mothers to amuse little children, or the widely-scattered mediaeval legends of the magician Merlin: he traces the mythology of the hearth down to the custom of the log which in Boccaccio's time at Florence the head of the family used to light upon the hearth at the new year, sprinkling incense and wine on it, and the Christmas-eve log among the lower classes at Naples; not to mention the custom in the Neapolitan kingdom of counting families by "hearths." He brought the serpent Python and all other mythical serpents into relation with the viper of the Visconti "che i milanesi accampa" ("which calls to arms the Milanese") and the hieroglyphic script with the _"rébus de Picardie"_ used in the north of France.