The subject of floating bridges having been discussed at one of the scientific parties which had assembled at the house of Salviati, a difference of opinion arose respecting the influence of the shape of bodies on their disposition to float or to sink in a fluid. Contrary to the general opinion, Galileo undertook to prove that it depended on other causes: and he was thus led to compose his discourse on floating bodies[18], which was published in 1612, and dedicated to Cosmo de' Medici. This work contains many ingenious experiments, and much acute reasoning in support of the true principles of hydrostatics; and it is now chiefly remarkable as a specimen of the sagacity and intellectual power of its author. Like all his other works, it encountered the most violent opposition; and Galileo was more than once summoned into the field to repel the aggressions of his ignorant and presumptuous opponents. The first attack upon it was made by Ptolemy Nozzolini, in a letter to Marzemedici, archbishop of Florence[19]; and to this Galileo replied in a letter addressed to his antagonist.[20] A more elaborate examination of it was published by Lodovico delle Colombe, and another by M. Vincenzo di Grazia. To these attacks, a minute and overwhelming answer was printed in the name of Benedetti Castelli, the friend and pupil of Galileo; but it was discovered, some years after Galileo's death, that he was himself the author of this work.[21]
The current of Galileo's life had hitherto flowed in a smooth and unobstructed channel. He had now attained the highest objects of earthly ambition. His discoveries had placed him at the head of the great men of his age; he possessed a professional income far beyond his wants, and even beyond his anticipations; and, what is still dearer to a philosopher, he enjoyed the most perfect leisure for carrying on and completing his discoveries. The opposition which these discoveries encountered, was to him more a subject for triumph than for sorrow. Prejudice and ignorance were his only enemies; and if they succeeded for a while in harassing his march, it was only to give him occasion for fresh achievements. He who contends for truths which he has himself been permitted to discover, may well sustain the conflict in which presumption and error are destined to fall. The public tribunal may neither be sufficiently pure nor enlightened to decide upon the issue; but he can appeal to posterity, and reckon with confidence on "its sure decree."
The ardour of Galileo's mind, the keenness of his temper, his clear perception of truth, and his inextinguishable love of it, combined to exasperate and prolong the hostility of his enemies. When argument failed to enlighten their judgment, and reason to remove their prejudices, he wielded against them his powerful weapons of ridicule and sarcasm; and in this unrelenting warfare, he seems to have forgotten that Providence had withheld from his enemies those very gifts which he had so liberally received. He who is allowed to take the start of his species, and to penetrate the veil which conceals from common minds the mysteries of nature, must not expect that the world will be patiently dragged at the chariot wheels of his philosophy. Mind has its inertia, as well as matter; and its progress to truth can only be insured by the gradual and patient removal of the obstructions which surround it.
The boldness—may we not say the recklessness?—with which Galileo insisted upon making proselytes of his enemies, produced the very opposite effect. Errors thus assailed, entrenched themselves in general feelings, and were embalmed in the virulence of the passions. The various classes of his opponents marshalled themselves for their mutual defence. The Aristotelian professors, the temporising Jesuits, the political churchmen, and that timid but respectable body who at all times dread innovation, whether it be in religion or in science, entered into an alliance against the philosophical tyrant who threatened them with the penalties of knowledge.
The party of Galileo, though weak in numbers, was not without power and influence. He had trained around him a devoted band, who idolised his genius and supported his views. His pupils had been appointed to several of the principal professorships in Italy. The enemies of religion were on this occasion united with the Christian philosopher; and there were, even in these days, many princes and nobles who had felt the inconvenience of ecclesiastical jurisdiction, and who secretly abetted Galileo in his crusade against established errors.
Although these two parties had been long dreading each other's power, and reconnoitring each other's position, yet we cannot exactly determine which of them hoisted the first signal for war. The church party, particularly its high dignitaries, were certainly disposed to rest on the defensive. Flanked on one side by the logic of the schools, and on the other by the popular interpretation of Scripture, and backed by the strong arm of the civil power, they were not disposed to interfere with the prosecution of science, however much they may have dreaded its influence. The philosophers, on the contrary, united the zeal of innovators with the firmness of purpose which truth alone can inspire. Victorious in every contest, they were flushed with success, and they panted for a struggle in which they knew they must triumph.
In this state of warlike preparation Galileo addressed a letter, in 1613, to his friend and pupil, the abbé Castelli, the object of which was to prove that the Scriptures were not intended to teach us science and philosophy. Hence he inferred, that the language employed in the sacred volume in reference to such subjects should be interpreted only in its common acceptation; and that it was in reality as difficult to reconcile the Ptolemaic as the Copernican system to the expressions which occur in the Bible.
A demonstration was about this time made by the opposite party, in the person of Caccini, a Dominican friar, who made a personal attack upon Galileo from the pulpit. This violent ecclesiastic ridiculed the astronomer and his followers, by addressing them in the sacred language of Scripture; "Ye men of Galilee, why stand ye here looking up into heaven?" But this species of warfare was disapproved of even by the church; and Luigi Maraffi, the general of the Dominicans, not only apologised to Galileo, who had transmitted to him a formal complaint against Caccini, but expressed the acuteness of his own feelings on being implicated in the "brutal conduct of thirty or forty thousand monks."
From the character of Caccini, and the part which he afterwards played in the persecution of Galileo, we can scarcely avoid the opinion that his attack from the pulpit was intended as a snare for the unwary philosopher. It roused Galileo from his wonted caution; and stimulated, no doubt, by the nature of the answer which he received from Maraffi, he published a longer letter of seventy pages, defending and illustrating his former views respecting the influence of scriptural language on the two contending systems. As if to give the impress of royal authority to this new appeal, he addressed it to Christian, grand-duchess of Tuscany, the mother of Cosmo; and in this form it seems to have excited a new interest, as if it had expressed the opinion of the grand-ducal family. These external circumstances gave additional weight to the powerful and unanswerable reasoning which this letter contains; and it was scarcely possible that any man, possessed of a sound mind, and willing to learn the truth, should refuse his assent to the judicious views of our author. He expresses his belief that the Scriptures were given to instruct mankind respecting their salvation, and that the faculties of our minds were given us for the purpose of investigating the phenomena of nature. He considers Scripture and nature as proceeding from the same divine author, and, therefore, incapable of speaking a different language; and he points out the absurdity of supposing that professors of astronomy will shut their eyes to the phenomena which they discover in the heavens, or will refuse to believe those deductions of reason which appeal to their judgment with all the power of demonstration. He supports these views by quotations from the ancient fathers; and he refers to the dedication of Copernicus's own work to the Roman pontiff, Paul III., as a proof that the pope himself did not regard the new system of the world as hostile to the sacred writings. Copernicus, on the contrary, tells his holiness, that the reason of inscribing to him his new system was, that the authority of the pontiff might put to silence the calumnies of some individuals, who attacked it by arguments drawn from passages of Scripture twisted for their own purpose.
It was in vain to meet such arguments by any other weapons than those of the civil power. His enemies saw that they must either crush the dangerous innovation, or allow it the fullest scope; and they determined upon an appeal to the inquisition. Lorini, a monk of the Dominican order, had already denounced to this body Galileo's letter to Castelli; and Caccini, bribed by the mastership of the convent of St. Mary of Minerva, was invited to settle at Rome for the purpose of embodying the evidence against Galileo.