The discovery of the satellites of Jupiter was called by Herschel "the holding turn of the Copernican system," but Galileo had no conception of its value; he passed it by as insignificant, and settled down complacently upon the flux and reflux of the tides as the crowning proof. To this proof, and to no other, he clung during the citation of 1616.
Astronomers express great surprise that Galileo makes no mention of the belts of Jupiter, although they are visible with the aid of the smallest glass.
Zucchi, a Jesuit, was the first to note them in Rome, (1630.) In like manner, the discovery of the spots on the sun do not appear to have benefited him in ascertaining the sun's rotation. "Galilée," says Arago, "n'a pas non plus la moindre apparence de droit à la découverte du mouvement de rotation du soleil. On a vu les taches; aucune conséquence de cette observation n'est indiquée." [Footnote 150]
[Footnote 150: "Neither has Galileo the slightest apparent claim to the discovery of the sun's rotation. The spots are observed, but no deduction is drawn from the observation.">[
The oversights concerning Jupiter are the more remarkable as Galileo's labors in investigation of the satellites were long and exhausting. It is only within a few years that this fact has been ascertained through the discovery by Professor Alberi of a long series of observations of the satellites of Jupiter, with tables and ephemerides drawn up for the purpose of comparing the longitude.
These manuscripts, described as a "mighty monument of his labors"—and doubtless they must be, for all his calculations were necessarily made without the aid of logarithms—were found in the Pitti Palace library, and are published by Alberi in the fifth volume of his magnificent edition of Galileo's work.
Herschel says that the science of astronomy was yet in its infancy at the period of Newton's death, and after all that Newton had done for it. What, then, must we think of its condition in the hands of Galileo, with his toy telescope, his fallacious tidal theory, and his necessary ignorance of the great discoveries that followed him?
In 1618, he published his Theory of the Tides. In 1623, he again puts it forward in a letter to Ingulfi; and finally devotes the fourth and last day of the Dialogue to the development of the same argument.
Nay, more, in this dialogue he scoffs at the simplicity of Kepler, who has had the temerity, after his (Galileo's) satisfactory explanation of the phenomena, to listen to such stuff as the occult properties of the moon's influence on the tides, and other like puerilities! We find by reference to a marginal note in the Padua edition of the Dialogues at the Astor Library, that a prelate, Girolamo Borro, wrote a pamphlet setting forth the theory of the moon's influence on the tides, and Simplicio is made to quote him: "E ultimamente certo prelato ha publicato un tratello dove dice che la luna vagando per il cielo attrae e solleva verso di se un cumulo d'acqua, il quale va continualmente seguitanclo," etc. [Footnote 151]