« 上一頁繼續 »
In the matter of hydraulics, Leonardo has hitherto passed for the inventor of many practical innovations, and also of a vast number of mere projects, the credit for which must be withdrawn from him in view of recent researches, especially those of Beltrami.
Take, for instance, his innovations in the making of locks.
According to Fumagalli, Leonardo invented the sluices contrived in lock gates, and substituted the sliding sash system of fixing them, for the vertical double doors on hinges. In short, he refers the whole modern system of working locks to Leonardo.
The truth is that the system of having practicable sluices in the gates of locks was made use of before the time of Leonardo. In 1481 the Venetians had constructed a lock on this system on the Piovego ; while Filippo Maria Visconti had caused one to be made as early as 1440 : “ Meditatus est et aquæ rivum, per quem ab Abbiate Viglevanum usque sursum veheretur, aquis altiora scandentibus machinarum arte, quas conchas appellant. . ..." “ It is obvious,” adds Venturi, “that the historian looked upon it as a common and well-known contrivance which had already received a name of its own.” In the Trattato d'Archittetura, compiled in 1450 at the very latest, L. B. Alberti describes the whole system in all its details. It is even possible that locks on this system were known as early as the fourteenth century.
Let us now turn to Leonardo's canals. Vasari declares that Leonardo, while still a youth,2 elaborated a scheme for a navigable canal between Florence and Pisa. He did not propose to embank and dredge the Arno, as Viviani did later, but to dig a separate canal, which should start from the Arno and traverse the districts of Prato, Pistoia,
nominati fu Gentile dei Borri, al quale Leonardo Vinci designo tutti gli uomini a cavallo, in qual modo potevano l'uno dallo altro defendersi con uno a piedi, ed ancora quelli che erano a piedi come si potevano l'uno e l'altro defendere ed offendere per cagioni delle diverse armi. La qual opera è stato veramente grandissimo danno che non sia stata data in luce per ornamento di questa stupendissima arte.” (Trattato, lib. vi. cap. xl.) The designs are believed to be those in the Trattato di Scienzia d'arme of the Milanese, Camillo Aggrippa (1553). (Amoretti, pp. 129-130.)
i Beltrami says that the famous architect and engineer of Siena, Francesco di Giorgio Martini, had described the system of coupled basins as early as 1447. But this date is clearly wrong, as Francesco was only born in 1439.
? According to Milanesi, this scheme dates from the year 1500. (Vasari, vol. iv., p. 89.)
Serravalle, and the lake of Sesto. Leonardo discusses the methods of supplying the canal with water, the cost of construction, the mode of dealing with the streams which cross it, etc. (Codex Atlanticus, f. 45-92.)
To Milan, cut off both from the great lakes and the main rivers of northern Italy, the question of inland navigation has been at all times vital. So the public gratitude to Leonardo, which credits him with the whole of these great works of canalisation, is easily understood.
"Under a burning sky”—I quote from Stendhal—“ Leonardo carried water into every corner of Milanese territory. It is to him the modern traveller owes the admirable landscapes, in which the fertility and verdure of the foreground are only equalled by the fantastic shapes of the snow-covered mountains, standing upon the distant horizon for the delight of the eye.” 1
Now as early as the twelfth century, Lombardy could boast of considerable hydraulic works, some for irrigation, some, very probably, for navigation. In the following century the waters of the Adda were drawn upon at Cassano to form the Muzza ; in the fourteenth, the stream taken from the Ticino was brought down to Milan, the canal to Pavia was made, and the Po was brought under proper control from Pont' Albero to the inouth of the Lambro.
The desire to connect Verbano, from which the marble used in building Milan Cathedral was drawn, with the centre of the capital, led, about the end of the fourteenth century, to the proposal to put the “Naviglio Grande” in direct communication with the great ditches by which the city was surrounded. To do this a difference of level of about five“ braccia” had to be neutralised. The level of the connecting canal was raised by suspending, at certain hours, all demands upon its water supply and by temporarily closing its outfall. As early as 1395 materials were thus transported “per navigium novum ad Logetum Sancti Stephani,” that is to say, to the reservoir communicating with the city moat.
This system, however, had one drawback : it interrupted for more or less lengthy intervals the supply of water for other purposes than navigation. Two locks were therefore constructed by which
1 Histoire de la Peinture en Italie.
the variations of level could be strictly confined to a part of the stream sufficient to contain the rafts and boats to be accommodated, and reservoirs were formed to enable the level of the water to be raised and lowered at will.
All Leonardo's biographers have shown a desire to claim for him the exclusive credit of having formed the Martesana canal. The dates, however, are stubborn. As early as 1457, when Leonardo was but five years old, Duke Francesco Sforza ordered this canal, which starts from the Adda, to be begun. One of his engineers,
Bertola da Novate,2 pushed on the work with such energy that the ducal government was able to proceed to the regular sale of the water brought down by the canal as early as 1465. Lodovico Il Moro also turned his attention to the Martesana. He not only proposed to increase its output of water, but also to make
it navigable as far as (Library of the Institut de France.)
the lake of Lecco. But
as the Adda makes a very long “détour" below Brivio, and as its stream is here too rapid, Lodovico thought it would be a good thing to make a canal above Brivio by which boats could descend, rejoining the Adda when the river again became navigable. The documents are silent as to the name of the engineer to whom this enterprise was entrusted. Neither does it appear that it was prosecuted with any great energy.
DESIGNS FOR WEAPONS.
1 An exception must be made in favour of Pagave, who has reduced Leonardo's share in the construction of this canal to its due proportions. (See Vasari, Delia Valle edition, vol. v., p. 63–64.)
2 Not Bertonino da Novara, as some have asserted.
In 1496 the engineering problems connected with it were still under discussion. Are we to credit Leonardo with the work? The fact is that, in 1496, Leonardo's name appears on the list of the duke's engineers, and he has left among his writings certain accounts of expenditure and notes of levels relating to the navigation of the Adda near Brivio. But we must add that from 1494 onwards, the name of Bartolommeo della Valle figures on the same list, and that the said Bartolommeo was the identical engineer to whom, with Benedetto da Massalia, was entrusted, in 1516, the expenditure of Francis I.'s subsidy of 10,000 ducats in aid of these very same works. It is natural to suppose that when the undertaking was commenced by Il Moro, it was also to him that the inauguration of the work was entrusted. 1
According to Beltrami, work on the Martesana may, then, be divided into two distinct periods; the first, before the arrival of Leonardo, corresponds to the making of the canal from Trezzo to Milan, for which Bertola da Novate was the engineer; the other period, posterior to Leonardo's departure for the French court, includes the studies and other preparations of Della Valle and De Massalia for the Paderno canal. Although described by Carlo Pagnano as early as 1520, this
i Leonardo da Vinci e il Naviglio Grande. My account of the various canals in the Milanese province attributed to Leonardo is borrowed from this work.
second enterprise was not completed until near the end of the sixteenth century, under the direction of Meda.
Beltrami's argument is close, as we must allow, and yet I feel some hesitation in admitting that Leonardo had nothing to do with the making of the Martesana. We have incontestable evidence that ten years later, between 1508 and 1510, he was directing important works on this very same water-way-works on which I shall have something to say in a future chapter
The Codex Atlanticus contains some further schemes for canals, such as those for a canal to unite Cesena with Porto Cesenatico, and for canals which were actually made in Friuli.
As for the scheme for a canal to be constructed near Romorontino, of that I shall have to speak in a chapter devoted to the activities of our artist-engineer in France.
I have now said enough to show that Leonardo was not only an Utopian dreamer, but that he was also an engineer of the greatest ability, to whom the science of hydraulics especially is indebted for much of the splendid progress it has made.
The making of canals has its natural pendant in undertakings for the raising and reclamation of the marshlands they traverse. Leonardo was not the inventor of the usual process employed for this purpose, for it had been practised in Tuscany as early as the twelfth century, but he was the first to give exact instructions for it.
Did Leonardo ever think of publishing the results of such arduous and fruitful investigations? The mystery with which, as engineer and theoretical mechanician, he so carefully surrounded himself, and the precautions he took against any undue filching from his manuscripts, prove at least that even if he kept publication in view as a final end, he was in no hurry meanwhile to give his discoveries to the world through the Press. Unlike his brother Florentine, Leone Battista Alberti, who took pride in writing for humanity at large, he wrote for himself. In a collection of scientific notes at Holkham is to be found a most suggestive declaration (made in connection with a sort of diving-dress) : “In view of the wickedness of men, I do not publish or divulge the method I have invented for remaining under water, for they (men)
1 “Non nobis sed humanitati scribimus."