stevie, As mentioned in a previous post the 1/4mps speed corresponds more closely to the velocity of Earth�s rotation at a latitude of 30�. Although about half the surface area of the Earth lies between north and south 30� latitudes the average velocity over the Earth's surface (about 1/4 mile in 1.36 seconds) corresponds more closely to the velocity of the Earth's rotation at 50� latitude.
Why either 1/4 mile or one second were chosen as suitable intervals is beyond me? I too have contemplated wildwood's suspicions. The internet is no longer solely the province of physicists, not that I�m complaining any!