The application of algebra to geometry ... has immortalized the name of Descartes, and constitutes the greatest single step ever made in the progress of the exact sciences.

So true is that unnatural generally means only uncustomary, and that everything which is usual appears natural.

Next to selfishness the principal cause which makes life unsatisfactory is want of mental cultivation.

The idea that truth always triumphs over persecution is one of those pleasant falsehoods, which most experience refutes. History is teeming with instances of truth put down by persecution. If not put down forever, it may be set back for centuries.

Ask yourself whether you are happy and you cease to be so. The only chance is to treat not happiness, but some end external to it, as the purpose of life.

It is given to no human being to stereotype a set of truths, and walk safely by their guidance with his mind's eye closed.

What distinguishes the majority of men from the few is their inability to act according to their beliefs.