Human subtlety will never devise an invention more beautiful, more simple or more direct than does nature because in her inventions nothing is lacking, and nothing is superfluous.
There are three classes of people: those who see, those who see when they are shown, those who do not see.
Iron rusts from disuse; water loses its purity from stagnation... even so does inaction sap the vigor of the mind.
Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory.
For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return.
I have been impressed with the urgency of doing. Knowing is not enough; we must apply. Being willing is not enough; we must do.
I love those who can smile in trouble, who can gather strength from distress, and grow brave by reflection. 'Tis the business of little minds to shrink, but they whose heart is firm, and whose conscience approves their conduct, will pursue their principles unto death.