The diversity of the phenomena of nature is so great and the treasures hidden in the heavens so rich 
precisely in order that the human mind shall never be lacking in fresh enrichment.
There is a force in the earth which causes the moon to move.
I much prefer the sharpest criticism of a single intelligent man to the thoughtless approval of the masses.
Geometry has two great treasures; one is the Theorem of Pythagoras; the other, the division of a line into extreme and mean ratio. The first we may compare to a measure of gold; the second we may name a precious jewel.
I used to measure the Heavens, now I measure the shadows of Earth. Although my mind was heaven-bound, the shadow of my body lies here.
Truth is the daughter of time, and I feel no shame in being her midwife.
Geometry is one and eternal shining in the mind of God.
We do not ask for what useful purpose the birds do sing, for song is their pleasure since they were created for singing. Similarly, we ought not to ask why the human mind troubles to fathom the secrets of the heavens. The diversity of the phenomena of nature is so great and the treasures hidden in the heavens so rich precisely in order that the human mind shall never be lacking in fresh nourishment.