There are in fact reasons for surmizing that in the cases alike of Bruno and of Vanini it was the attitude of the speculator towards scientific problems that primarily or mainly aroused distrust and anger among the theologians. Vanini is careful to speak equivocally of the eternity of the universe; and though he makes a passing mention of Kepler, [251] he does not name Copernicus. He had learned something from the fate of Bruno. Yet in the Dialogue De coeli forma et motore [252] he declares so explicitly for a naturalistic explanation of the movements of the heavenly bodies that he must have aroused in some orthodox readers such anger as was set up in Plato by a physical theory of sun and stars. After an à priori discussion on Aristotelian lines, the querist in the dialogue asks what may fitly be held, with an eye to religion, concerning the movements of the spheres. "This," answers Vanini, "unless I am in error: the mass of the heaven is moved in its proper gyratory way by the nature of its elements." "How then," asks the querist, "are the heavens moved by certain and fixed laws, unless divine minds, participating in the primal motion, there operate?" "Where is the wonder?" returns Vanini. "Does not a certain and fixed law of motion act in the most paltry clockwork machines, made by a drunken German, even as there works silently in a tertian and quartan fever a motion which comes and goes at fixed periods without transgressing its line by a moment? The sea also at certain and fixed times, by its nature, as you peripatetics affirm, is moved in progressions and regressions. No less, then, I affirm the heaven to be forever carried by the same motion in virtue of its nature (a sua pura forma) and not to be moved by the will of intelligence." And the disciple assents. Kepler had seen fit, either in sincerity or of prudence, to leave "divine minds" in the planets; and Vanini's negation, though not accompanied by any assertion of the motion of the earth, was enough to provoke the minds which had only three years before put Copernicus on the Index, and challenged Galileo for venting his doctrine.