The light and heat of the universe comes from the sun, and its cold and darkness from the withdrawal of the sun.

Nature is constrained by the cause of her laws which dwell inborn in her. Variant: Nature is constrained by the order of her own law which lives and works within her.

O sleepers! what a thing is slumber! Sleep resembles death. Ah, why then dost thou not work in such wise as that after death thou mayst retain a resemblance to perfect life, when, during life, thou art in sleep so like to the hapless dead?

Every action needs to be prompted by a motive.

One painter ought never to imitate the manner of any other; because in that case he cannot be called the child of nature, but the grandchild. It is always best to have recourse to nature, which is replete with such abundance of objects, than to the productions of other masters, who learnt everything from her.

The earth is moved from its position by the weight of a tiny bird resting upon it.

It is useful to constantly observe, note, and consider.