How to draw a straight line

Copeland Crack aims to be at the very least useful.

Peaucellier's solution to the riddle

So I'm happy to pass on a book I have discovered: How To Draw A Straight Line. And best of all it is free courtesy of Project Gutenberg (a wonderful project of which more in a later blog). Now I know what you're thinking. 1. Pick up a pen; 2. Pick up a ruler; 3. Draw a straight line. And indeed there is an article along those very lines (if you'll pardon the pun) at Wikihow. There's even a drawing of a straight line with the caption: Making a straight line like this is possible.

But the book on how to draw a straight line to which I refer is more subtle, more magical and much more interesting than that. The book by A B Kempe was first published in 1877 and publicised the marvellous discovery by French army officer, Charles-Nicolas Peaucellier (1832 - 1913). He got his mind round the previously unsolved engineering riddle of turning a rotary action - such as a mill wheel - through various cranks and shafts into a force that was going in a linear motion. I doubt the animated gif will work on our website but if you watch it on Wikipedia you'll find it quite hypnotic. Lord Kelvin on seeing the device said: "it is the most beautiful thing I have ever seen in my life." Thanks to Kempe and others the little-known discovery received wider publicity and fame.