We can only penetrate the rind of the earth.

There is nothing good in love but the physical part.

Only those works which are well-written will pass to posterity: the amount of knowledge, the uniqueness of the facts, even the novelty of the discoveries are no guarantees of immortality ... These things are exterior to a man but style is the man himself.

There are several kinds of truths, and it is customary to place in the first order mathematical truths, which are, however, only truths of definition. These definitions rest upon simple, but abstract, suppositions, and all truths in this category are only constructed, but abstract, consequences of these definitions ... Physical truths, to the contrary, are in no way arbitrary, and do not depend on us.

In Ireland, there are the same fossils, the same shells and the same sea bodies, as appear in America, and some of them are found in no other part of Europe.

To write well is to think well, to feel well, and to render well; it is to possess at once intellect, soul, and taste.

All the work of the crystallographers serves only to demonstrate that there is only variety everywhere where they suppose uniformity ... that in nature there is nothing absolute, nothing perfectly regular.