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38 seeing the early inverting pattern. His microscopes were soon as much in demand as his telescopes, as they were much more powerful and gave better definition than those previously made.

There is no doubt that he was all the time pining for a favourable opportunity of openly defending the Copernican system. An attack made on it by Ingoli in 1616, addressed to Galileo, had remained unanswered at the time, owing to the hostile attitude of the Inquisition. Kepler answered it in 1618 in his "Epitome of the Copernican Astronomy," but Galileo felt that he might now venture to reply more fully, taking special precautions to emphasise the point that he was merely treating the system as a working hypothesis. He professed to have two objects in view, one personal, to clear himself from the suspicion of having propounded an absurd and irreligious theory, by showing that he had supported it before it was under theological ban, and that from every other point of view it was quite reasonable and probable; the other, from a sense of loyalty to Church and country, to give the Protestant Copernicans of Germany the true explanation of the apparent rejection of their system in Italy. On the advice of friends he only circulated his reply in manuscript, and was told that the Pope approved of it after hearing passages read, saying that the Church had not condemned the Copernican doctrine as heretical, but as rash.

It is not at all surprising that this and other similar encouraging reports should have convinced Galileo that the time was getting ripe for the complete victory of the new system, provided that it advanced cautiously at first. So for the next four years, 1626 to 1629, he did little else, in the intervals between frequent attacks of illness and domestic troubles, but concentrate his energies on the production of his most imposing astronomical work,