Astronomy is perhaps the science whose discoveries owe least to chance, in which human understanding appears in its whole magnitude, and through which man can best learn how small he is.

Sickness is mankind's greatest defect.

Reason now gazes above the realm of the dark but warm feelings as the Alpine peaks do above the clouds. They behold the sun more clearly and distinctly, but they are cold and unfruitful.

The most successful tempters and thus the most dangerous are the deluded deluders.

When a book and a head collide and a hollow sound is heard, must it always have come from the book?

The more experiences and experiments accumulate in the exploration of nature, the more precarious the theories become. But it is not always good to discard them immediately on this account. For every hypothesis which once was sound was useful for thinking of previous phenomena in the proper interrelations and for keeping them in context. We ought to set down contradictory experiences separately, until enough have accumulated to make building a new structure worthwhile.

Never undertake anything for which you wouldn't have the courage to ask the blessings of heaven.