scattered materials of his scientific system, and I may venture to
state that I have devoted especial care and thought to the due
execution of this responsible task.

The beginning of Leonardo's literary labours dates from about his
thirty-seventh year, and he seems to have carried them on without
any serious interruption till his death. Thus the Manuscripts that
remain represent a period of about thirty years. Within this space
of time his handwriting altered so little that it is impossible to
judge from it of the date of any particular text. The exact dates,
indeed, can only be assigned to certain note-books in which the year
is incidentally indicated, and in which the order of the leaves has
not been altered since Leonardo used them. The assistance these
afford for a chronological arrangement of the Manuscripts is
generally self evident. By this clue I have assigned to the original
Manuscripts now scattered through England, Italy and France, the
order of their production, as in many matters of detail it is highly
important to be able to verify the time and place at which certain
observations were made and registered. For this purpose the
Bibliography of the Manuscripts given at the end of Vol. II, may be
regarded as an Index, not far short of complete, of all Leonardo s
literary works now extant. The consecutive numbers (from 1 to 1566)
at the head of each passage in this work, indicate their logical
sequence with reference to the subjects; while the letters and
figures to the left of each paragraph refer to the original
Manuscript and number of the page, on which that particular passage
is to be found. Thus the reader, by referring to the List of
Manuscripts at the beginning of Volume I, and to the Bibliography at
the end of Volume II, can, in every instance, easily ascertain, not
merely the period to which the passage belongs, but also exactly