Quotes About Covariance

Einstein enunciated what he called the Principle of Covariance: that laws of Nature should be expressed in a form that will look the same for all observers, no matter where they are located and no matter how they are moving.

Can you imagine my joy at the feasibility of the general covariance with the result that the equations of the perihelion movement of Mercury prove correct? I was speechless for several days with excitement. (Einstein to Ehrenfest)