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Rh matter also, Galileo's consent being noted accordingly in the minute. The probability of this view, which is practically that of Professor Favaro, the most diligent student of Galileo at the present day, is much increased by the fact that the minute was not signed. In the event, as we shall see, this weakness of evidence was ignored.

Galileo was assured by the Pope himself that his fears of continual persecution were groundless, but the Tuscan ambassador felt that Galileo was doing himself no good by staying on at Rome and arguing with people, so he gave a hint to his master, and Cosmo recalled Galileo to Florence.

While at Rome Galileo had found time to write to Cardinal Orsini a treatise on the tides, afterwards amplified in his great work on the two systems of the world, to which we shall refer later. He also made definite proposals to the Court of Spain upon a new method of determining longitude, which would be of great importance to a seafaring nation. Ever since his discovery of Jupiter's moons, with their frequent eclipses, he had kept in view the possibility of accurately predicting these phenomena, and had observed for six years with a view to perfecting his tables of their movements. His idea was that local time being determined by observing the sun at noon, the further observation of the time of one of these eclipses in Jupiter's system, compared with that given in the tables, would give the difference of longitude between the observer and the place for which the tables were computed. The negotiations with the Spanish Court led to nothing, owing partly to the difficulty of obtaining the observations on a moving ship, and to the absence of reliable chronometers to carry on the local time from noon till dark. The Grand Duke tried the method in the Tuscan Navy, but it was practically a failure.