Sense is given to it solely because it is the common judge of all the other five senses i.e. Seeing, Hearing, Touch, Taste and Smell.  This Common Sense is acted upon by means of Sensation which is placed as a medium between it and the senses.  Sensation is acted upon by means of the images of things presented to it by the external instruments, that is to say the senses which are the medium between external things and Sensation.  In the same way the senses are acted upon by objects.  Surrounding things transmit their images to the senses and the senses transfer them to the Sensation.  Sensation sends them to the Common Sense, and by it they are stamped upon the memory and are there more or less retained according to the importance or force of the impression.  That sense is most rapid in its function which is nearest to the sensitive medium and the eye, being the highest is the chief of the others.  Of this then only we will speak, and the others we will leave in order not to make our matter too long.  Experience tells us that the eye apprehends ten different natures of things, that is:  Light and Darkness, one being the cause of the perception of the nine others, and the other its absence:—­ Colour and substance, form and place, distance and nearness, motion and stillness [Footnote 15:  Compare No. 23.].

On the origin of the soul.

837.

Though human ingenuity may make various inventions which, by the help of various machines answering the same end, it will never devise any inventions more beautiful, nor more simple, nor more to the purpose than Nature does; because in her inventions nothing is wanting, and nothing is superfluous, and she needs no counterpoise when she makes limbs proper for motion in the bodies of animals.  But she puts into them the soul of the body, which forms them that is the soul of the mother which first constructs in the womb the form of the man and in due time awakens the soul that is to inhabit it.  And this at first lies dormant and under the tutelage of the soul of the mother, who nourishes and vivifies it by the umbilical vein, with all its spiritual parts, and this happens because this umbilicus is joined to the placenta and the cotyledons, by which the child is attached to the mother.  And these are the reason why a wish, a strong craving or a fright or any other mental suffering in the mother, has more influence on the child than on the mother; for there are many cases when the child loses its life from them, &c.

This discourse is not in its place here, but will be wanted for the one on the composition of animated bodies—­and the rest of the definition of the soul I leave to the imaginations of friars, those fathers of the people who know all secrets by inspiration.

[Footnote 57:  lettere incoronate.  By this term Leonardo probably understands not the Bible only, but the works of the early Fathers, and all the books recognised as sacred by the Roman Church.] I leave alone the sacred books; for they are supreme truth.