On a modern piano (in well-tempered tuning) the interval between do-re and re-mi are equal in size. Can they be equal in size if we use the harmonic series to make re-fa a minor third and re-sol a perfect fourth? (With size I mean how big the interval is between two notes in percent. An examole would be from A1 to A2 we have an octave and A5 to A6 is also an octave in size.)
If I sing a chord eg Do-mi-sol I would use the perfect intervals from the harmonic series. How would the harmonic series fit with the intervals of major seconds?