High astronomical authority, Délambre, thus sums up the utter absence of proof, in Galileo's time, of the theory of the earth's rotation:
"What solid reason could induce the ancients to disbelieve the evidence of their senses? Yes, and even despite the immense progress which astronomy has subsequently made, have the moderns themselves been able to allege any one direct proof of the diurnal motion of the earth, previous to the voyage of Richer to Cayenne, where he was obliged to shorten his pendulum? Have they been able to discover one positive demonstration to the point, to prove the annual revolution of the earth, before Roemer measured the velocity of light, and Bradley had observed and calculated the phenomena of the aberration?
"Previous to these discoveries, and that of universal gravitation, were not the most decided Copernicans reduced to mere probabilities? Were they not obliged to confine themselves to preaching up the simplicity of the Copernican system, as compared with the absurd complexity of that of Ptolemy?"
What "solid reason," indeed, could be given? But Galileo in his presumption did not consider himself reduced to "mere probabilities," and, relying on his tidal fallacies and unexplained phenomena, sought to pass hypothesis for dogma, and his ipse dixit for demonstration.
Of the great discoveries enumerated by Délambre, Galileo was necessarily ignorant, and we must insist upon the fact that the cardinals and the Inquisition were equally ignorant of them.
There was, in reality, no astronomical science in Galileo's time worth speaking of, except as we compare it with the astronomy that preceded it, which is the only fair test of its value. Compared with what Ptolemy knew, it was twilight.
Compared with what we know, it was darkness.
It is moderate to say that in 1633 astronomy was in its infancy. To all that was then known, add Kepler's magnificent labors, Torricelli's discovery, Newton's principle of gravitation, and all the English astronomer did for science—come down to the year 1727, in which he died, and what was the condition of astronomical science even then?
Herschel has told us: "The legacy of research which was left us by Newton was indeed immense. To pursue through all its intricacies the consequences of the law of gravitation; to account for all the inequalities of the planetary movements, and the infinitely more complicated and to us more important ones of the moon; and to give, what Newton himself certainly never entertained a conception of, a demonstration of the stability and permanence of the system under all the accumulated influence of its internal perturbations; this labor and this triumph were reserved for the succeeding age, and have been shared in succession by Clairault, D'Alembert, Euler, Lagrange, and Laplace. Yet so extensive is this subject, and so difficult and intricate the purely mathematical inquiries to which it leads, that another century may yet be required to go through the task."