Pliny has preserved an anecdote in geological history, which relates to this point, and which, not without reason, he calls _exemplum vanitatis Græcæ maximum_. It relates to a certain philosopher, Dionysiodorus by name, who was celebrated for his mathematical attainments, and who it seems retained his attachment to that science after death, and continued the pursuit of it. For having died in a good old age, and received all fitting sepulchral rites, he wrote a letter from Hades to the female relations who had succeeded to his property, and who probably were addicted to the same studies as himself, for otherwise he would not have communicated with them upon such a subject. They found the letter in his sepulchre, wherein he had deposited it as at a post-office “till called for;” and whither he knew they would repair for the due performance of certain ceremonies, among others that of pouring libations through the perforated floor of the Tomb-chamber upon the dust below. The purport of his writing was not to inform them of his condition in the Shades, nor to communicate any information concerning the World of Spirits, but simply to state the scientific fact, that having arrived in the depths of the earth, he had found the distance from the surface to be 42,000 stadia. The philosophers to whom this _post-mortem_ communication was imparted, reasonably inferred that he had reached the very centre, and measured from that point; they calculated upon the data thus afforded them, and ascertained that the globe was exactly 250,000 stadia in circumference. Pliny however thought that this measurement was 12,000 stadia short of the true amount. _Harmonica ratio_, he says, _quæ cogit rerum naturam sibi ipsam congruere, addit huic mensuræ stadia xii. millia; terramque nonagesimam sextam totius mundi partem facit._ “What is the centre of the earth?” says the melancholy Burton. “Is it pure element only as Aristotle decrees? Inhabited, as Paracelsus thinks, with creatures whose chaos is the earth? Or with Faeries, as the woods and waters, according to him, are with Nymphs? Or, as the air, with Spirits? Dionysiodorus,” he adds, “might have done well to have satisfied all these doubts?”