"But whoever may have still felt inclined... in the face of this almost overwhelming agreement... to believe it... a coincidence, must... give up... doubt when A. Sommerfeld deduced, by a logical extension of the laws of the distribution of quanta in systems with several degrees of freedom, and by a consideration of the variability of inert mass required by the principle of relativity, that magic formula before which the spectra of both and revealed the mystery of their ... by the most delicate measurements...of F. Paschen..."