Regarding Chris May's letter (NCE last week), I think his calculations for the speed of the earth in its orbit around the Sun are suspect.
Taking the orbit as circular, with a radius of 92M miles, the more accepted figure for the Earth's distance from the Sun, the distance travelled around the Sun in one year, would be 2p x 92M = 577,760,000 miles (that is, over twice May's value).
The distance travelled by the Earth in one day would then be 577,760,000 / 365 = 1,582,904 miles, so the velocity along its orbit is 1,582,904 / 24 = 65,954mph.
In fact, the Earth's orbit is elliptical with the Sun as one of the foci, so the distance is greater than the foregoing estimate, therefore, the speed we are travelling around the sun is probably in excess of 70,000mph.
Maurice Baguley (ret F), The Barn, Ivy Mill Lane, Godstone, Surrey RH9 8NF