One can descend by imperceptible degree from the most perfect creature to the most shapeless matter, from the best-organised animal to the roughest mineral.

Time is the great workman of Nature.

For the little that one has reflected on the origin of our knowledge, it is easy to perceive that we can acquire it only by means of comparison. That which is absolutely incomparable is wholly incomprehensible. God is the only example that we could give here. He cannot be comprehended, because he cannot be compared. But all which is susceptible of comparison, everything that we can perceive by different aspects, all that we can consider relatively, can always be judged according to our knowledge.

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.

Although the works of the Creator may be in themselves all equally perfect, the animal is, as I see it, the most complete work of nature, and man is her masterpiece.

The cat is the only animal which accepts the comforts but rejects the bondage of domesticity.

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.