The evolution of power-line frequencies 133 1/3 to 25 Hz

It is generally understood that 60 Hz as frequency of AC power, has not always been that number. 60 Hz resulted after several trials of values for AC frequency, each determined by different criteria. This article presents a brief overview of the various frequencies beginning with 133 1/3 Hz and traveling through 125, 83 1/3, 66 2/3, 60, 50, 40, 30, and 25 Hz. They did not appear in the chronological order listed here, and their selection was influenced, to a great degree, by the types of applications made of electrical power during the early period of electrical technology.