The minor third is a factor of 1.2 in a just intonation scale, and a major third is a factor of 1.25. From the graph in Roderer's book noted above, the most consonant interval is about 1.27 for which there isn't a close scale note, but 1.25 is pretty close. That minor third is about the minimum consonant interval. 4 of them successively is the diminished 7th.