296 



NA TURE 



[January 26, 1893 



year 1320, he seems to have gone for some unknown reason 

 to Mantua, and there to have entered upon this discussion, 

 which he then completed at Verona. The disputation 

 took place at this latter city on January 20, 1320, as Dante 

 himself tells us, in the church of St. Helena (where in 

 recent years the metropolitan chapter have put up a 

 monument in commemoration of the event). All the 

 clergy of Verona were present, except some few who, in 

 the words of Rossetti — 



" Grudged ghostly greeting to the man 

 By whom, though not of ghostly guild, 

 With Heaven and Hell men's hearts were fiU'd." 



— " Dante at Verona." 



From a passage which occurs in the course of the 

 treatise, one might almost think that ladies also were 

 present, but let not the reader therefore conclude that the 

 assemblage which listened to Dante's eloquence in that 

 little Veronese temple resembled so many modern philan- 

 thropical and other associations in being chiefly composed 

 of ladies and clergymen, for doubtless Can Grande della 

 Scala himself was present to do honour to his former 

 guest, and his poetic fame, which we know to have already 

 spread far and wide, would certainly have brought together 

 as many as the church could hold. 



The question to be solved is whether, on any place on 

 the earth's surface, water is higher than the earth. This 

 question, Dante tells us, was generally answered in the 

 affirmative, and he gives us the five chief reasonings 

 adduced in support of it, of which perhaps the most 

 striking is this one : — 



" If the earth were not lower than the water, the earth 

 would be entirely without waters, at least in the uncovered 

 part, and so there would be no fountains, nor rivers, nor 

 lakes. So water must be higher than the earth. For 

 water naturally flows downwards, and the sea is the source 

 of all waters, and if the sea were not higher than the 

 earth, the water would not flow to the earth, since in 

 every natural motion the source of the water must be 

 higher." 



Another is this :— " Water seems chiefly to follow the 

 motion of the moon, as is evident in the flow and ebb of 

 the sea, and therefore since the moon's orbit is eccentric, 

 it seems reasonable that water in its sphere should be 

 eccentric too ; and another argument shows that this 

 cannot be unless it be also higher than the earth." 



Such be their arguments, but sense and reason alike 

 are against them, and Dante proceeds to explain how he 

 will treat the question. First, he will prove that it is im- 

 possible that water in any part of its circumference be 

 higher than this emergent or uncovered earth on which 

 we dwell. Secondly, he will prove that this emergent 

 earth is everywhere higher than the surface of the sea. 

 Thirdly, he will urge arguments against his own demon- 

 strations, and then demolish these objections. Fourthly, 

 the final and efficient cause of the elevation and emergence 

 of the earth will be shown. Fifthly, he will demolish the 

 five chief arguments of the other side which he has 

 already stated. 



I. It is impossible that water in any part of its circum- 

 ference be higher than the earth. 



There are only two ways whereby water can thus be 

 higher than the earth : either the water must be eccentric, 

 or, if it be concentric with the earth, it must h& gibbous in 

 some part. By water being eccentric, Dante means the 

 centre of its natural sphere to be out of and different from 

 the centre of the earth ; by being gibbous, Dante means 

 some part of its sphere to be raised up so as to form a 

 protuberance or hump, just as he considers the earth on 

 which we live to be a protuberance or gibbosity of the 

 spherical surface of the earth. 



He now shows by means of diagrams that neither of 

 these things are possible, but first makes these two state- 

 ments — (i) Water naturally flows downwards ; (2) Water 



NO. I 2 13, VOL. 47] 



is by nature a labile body and has not a boundary of its 

 own, but takes the boundary of the thing in which it is 

 contained.^ 



We may compare with this a modern definition of a 

 fluid :— 



" A perfect fluid is a body whose form can be changed 

 to any extent, provided its volume remain constant, by 

 the application of a stress, however small, if we allow it 

 sufficient time.''— Garnett, " Treatise on Heat." 



In the first place, water cannot be eccentric. 



For if it were so, then three impossibilities would follow 

 — (i) Water would naturally flow both upwards and down- 

 wards ; (2) water would not be moved downwards by the 

 same line as the earth ; (3) an equivocation would arise 

 in speaking of the gravity of water and of earth ; all 

 which things are seen to be not only false but im- 

 possible. 



The demonstration ab absurdo follows thus : — Let the 

 heavens be the circumference on which are placed three 

 crosses; water the circumference on which are two; 

 earth the circumference on which is one cross. 



Let the centre of heaven and earth be at point A, the 

 centre of water at point B. Thus A, being the centre of 

 the universe, is the lowest spot of all, and everything 

 which has in the world a position alien from A must be 

 higher. Now if there be any water at A and the way be 

 open to it, it will naturally flow to its own centre, B, since 

 it is the property of every heavy body to move to the 

 centre of its own sphere. But the motion from A to B is 

 a motion upwards ; therefore water will flow upwards, 

 which is impossible. 



Again, let there be at z a lump of earth and some water, 

 and let there be nothing to hinder. Then, since it is the 

 property of every heavy body to move to the centre of its 

 own sphere or circumference, the earth will move in a 

 straight line to A, and the water in a straight line to B, 

 and this, from the figure, must needs be along different 

 lines. This, says Dante, is not only impossible, but 

 would make Aristotle laugh if he were to hear it. 



The third impossibility follows thus -.—Gravity and 

 levity are " passions" of simple bodies which are moved 

 with linear motion, and light bodies tend upwards and 

 heavy tend downwards, by " heavy " and " light " being 

 meant that which has the power of being moved. If now 

 water moved to B and earth to A, since these are simple 

 bodies and heavy, they will be moved down to different 

 centres. If this were so, the \^ ox A gravity wovXd. have 

 an absolute signification with respect to earth and relative 

 with respect to water. This is what the argument amounts 

 to, and so there would be an equivocation of meaning in 

 the word "gravity." 



Therefore, ab absurdo, water in its natural circumfer- 

 ence is not eccentric or out of ^^the centre common to the 

 circumference of the earth. 



In the second place, water cannot be gibbous. 



' " Aqua est labile corpus naturaliter, et non terminabile termino proprio." 



