YOUR OPINIONS ON SCIENCE, TECHNOLOGY AND OUR MAGAZINE
LETTER OF THE MONTH
In the shadows
In ‘The Counterintuitive Cosmos’ (February, p73) you mentioned Eratosthenes measuring the size of the Earth. He would have needed an accurate measurement of the distance from Alexandria to Syene, about 1,000km (620 miles) and a very accurate way of measuring time. How could he have done this?
Anthony Fenwick-Wilson, Shropshire
Marcus Chown replies: Ancient people were smart! While working at the library in Alexandria, Eratosthenes learned that on the first day of summer there were no shadows cast in the Egyptian town of Syene. So he needed only to observe the shadow of a vertical pillar at Alexandria on the same day. He made his estimate of the distance between Alexandria and Syene from the time it took walkers, who were trained to measure distances by taking regular strides, to trek between the cities.
WRITE IN AND WIN!
The writer of next issue’s Letter of the Month wins a pair of popular science books. Put pen to paper and you could win Mapmatics and Space Oddities.
Solving the pothole problem
I noted all the high-tech solutions to the problems of weather extremes destroying Tarmac (February, p36). In France, Napoleon planted lines of trees alongside the roads to shade his marching troops. It has been my observation, in France and in the UK, that such shade prevents Tarmac from melting in summer and protects it from frost
