As Leonardo was born in 1452, he says, we may presume his mind to have been in full expansion before 1490. His Treatise on Painting is known as a very early disquisition of the rules of the art. But his greatest literary distinction is derived from those short fragments of his unpublished writings that appeared not many years since; and which, according, at least, to our common estimate of the age in which he lived, are more like revelations of physical truths vouchsafed to a single mind, than the superstructure of its reasoning upon any established basis. The discoveries which made Galileo, and Kepler, and Mæstlin, and Maurolycus, and Castelli, and other names illustrious, the system of Copernicus, the very theories of recent geologers, are anticipated by Da Vinci, within the compass of a few pages, not perhaps in the most precise language, or on the most conclusive reasoning, but so as to strike us with something like the awe of preternatural knowledge.
In an age of so much dogmatism, he first laid down the grand principle of Bacon, that experiment and observation must be the guides to just theory in the investigation of nature. If any doubt could be harboured, not as to the right of Leonardo da Vinci to stand as the first name of the fifteenth century, which is beyond all doubt, but as to his originality in so many discoveries, which, probably, no one man, especially in such circumstances, has ever made, it must be on a hypothesis, not very untenable, that some parts of physical science had already attained a height which mere books do not record. The extraordinary works of ecclesiastical architecture in the Middle Ages, especially in the fifteenth century, as well as those of Toscanelli and Fioravanti, which we have mentioned, lend some countenance to this opinion; and it is said to be confirmed by the notes of Fra Mauro, a lay brother of a convent near Venice, on a planisphere constructed by him, and still extant. Leonardo himself speaks of the earth’s annual motion, in a treatise that appears to have been written about 1510, as the opinion of many philosophers in his age.[f]
Among the almost numberless scraps of manuscript left us by Leonardo is a letter which he addressed to Ludovico il Moro, duke of Milan, in 1483. The original of this letter exists in the author’s own orthography, and it gives his own estimate of his accomplishments at the age of thirty-one. It will be borne in mind, of course, that this letter is addressed to a prince who would be likely to value the services of a practical engineer more than those of a mere painter. This, no doubt, explains in part the subordinate place given to Leonardo’s capacity as sculptor and painter, which, as will be seen, is only mentioned after ten other specifications. Nevertheless, it was while in Milan that Leonardo executed his greatest work, the famous Last Supper. The letter is as follows:[a]
Having seen and sufficiently considered the works of all those who repute themselves to be masters and inventors of instruments for war, and found that the form and operation of these works are in no way different from those in common use, I permit myself, without seeking to detract from the merit of any other, to make known to your excellency the secrets I have discovered, at the same time offering with fitting opportunity, and at your good pleasure, to perform all those things which, for the present, I will but briefly note below.
(1) I have a method of constructing very light and portable bridges, to be used in the pursuit of, or retreat from, the enemy, with others of a stronger sort, proof against fire or force, and easy to fix or remove. I have also means for burning and destroying those of the enemy.
(2) For the service of sieges, I am prepared to remove the water from the ditches, and to make an infinite variety of fascines, scaling-ladders, etc., with engines of other kinds proper to the purposes of a siege.
(3) If the height of the defences or the strength of the position should be such that the place cannot be effectually bombarded, I have other means, whereby any fortress may be destroyed, provided it be not founded on stone.
(4) I have also most convenient and portable bombs, proper for throwing showers of small missiles, and with the smoke thereof causing great terror to the enemy, to his imminent loss and confusion.
(5) By means of excavations made without noise, and forming tortuous and narrow ways, I have means of reaching any given ... (point?), even though it be necessary to pass beneath ditches or under a river.
(6) I can also construct covered wagons, secure and indestructible, which, entering among the enemy, will break the strongest bodies of men; and behind these the infantry can follow in safety and without impediment.