It is unnecessary to go here over the ground occupied by our author in his preliminary _brochure_, and to give the history of the MSS. in question. Suffice it to say that at an early time they were scattered throughout the principal collections in Europe, and that the fears entertained by Leonardo da Vinci himself respecting the non-publication of his numerous treatises on art and on science seemed likely to be fulfilled. No sooner had death removed Francisco Melzi, Leonardo’s favourite pupil and friend, than the invaluable codices entrusted to his care were dispersed and mutilated; as even one single page would fetch a considerable sum of money, the MSS. were broken up into small fragments, so as to satisfy the curiosity of the greatest possible number of amateurs; and in order to obtain any given work in its complete form, it would be necessary to seek the elements of that work at Milan, Windsor, and Kensington. Numerous treatises have thus been lost or are perhaps buried under the dust of public and private libraries, and the materials now at our disposal represent only a small part of the whole collection, such as Francisco Melzi originally possessed it, and such as in all probability the artistic world will not see it again. By a piece of singular good luck the “Institut de France” possesses twelve volumes of Leonardo da Vinci’s writings; they were indexed towards the end of the last century by an Italian _savant_, named Venturi, who had examined them carefully, and had even published some extracts from them; these volumes are lettered A--M, and have the great merit of giving the consecutive views of the author on the subjects which he had studied. This point is of the highest importance in the case of a man such as Leonardo da Vinci, who lost no opportunity of showing the interdependence of the several branches of science, and the light they all throw upon one another. M. Ravaisson-Mollien has accordingly undertaken the arduous task of editing the entire works of Leonardo da Vinci, so far at least as they are known to exist, and we earnestly trust that he may be able to accomplish his rather ambitious design.