It is of the highest importance in the art of detection to be able to recognise out of a number of facts which are incidental and which are vital.

The world is full of obvious things which nobody by any chance ever observes.

Love has been taken away from the poets, and has been brought within the domain of true science. It may prove to be one of the great cosmic elementary forces. When the atom of hydrogen draws the atom of chlorine towards it to form the perfected molecule of hydrochloric acid, the force which it exerts may be intrinsically similar to that which draws me to you. Attraction and repulsion appear to be the primary forces. This is attraction.

There is nothing like first-hand evidence.

I am an omnivorous reader with a strangely retentive memory for trifles.

Art in the blood is liable to take the strangest forms.

I consider that a man's brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. [...] It is a mistake to think that that little room has elastic walls and can distend to any extent. [...] It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.