The eye transmits its own image through the air to all the objects which face it, and also receives them on its own surface, whence the "sensus communis" takes them and considers them.

Oh! Speculators on things, boast not of knowing the things that nature ordinarily brings about; but rejoice if you know the end of those things which you yourself device.

Iron rusts from disuse; water loses its purity from stagnation... even so does inaction sap the vigor of the mind.

Learning never exhausts the mind.

There shall be wings! If the accomplishment be not for me, 'tis for some other. The spirit cannot die; and man, who shall know all and shall have wings.

The eye - which sees all objects reversed - retains the images for some time.

Anyone who invokes authors in discussion is not using his intelligence but his memory.