Foreword by Henri Michel 

As a specialist, I have read most of the books about sundials and yes I must sincerely recommend this one and congratulate the author on it.

Formerly a ship captain, René R.J.ROHR had already revealed himself as a fine observer and as a person extremely sensitive to the beauty of things in his books on travel. He is therefore well equipped to pass judgement on an instrument that is simultaneously scientific, historical, and artistic. His lively pen, his direct and simple style, his expressive vocabulary, his avoidance of pedantry, his conciseness in the exposition of his thoughts make his book a pleasure to read.

Too many writers, in dealing with this topic, would have accumulated the references or exhibited their erudition, or even taken a detached attitude of superiority. René R. J.ROHR knows that true humility consists in ignoring one's own humbleness and never taking pride in it. He thinks first about his reader, of what will interest him. He does not try to teach: he only wants us to develop understanding.

            Once we have read these lively, picturesque, and clearly written pages, once we have gained a precise idea of this gnomonics which has attracted so many mathematicians, we will feel much sympathy for the author. Indeed he has fulfilled the three conditions required for a good book: have something to say; say it; don't say anything else.

                               Henri Michel, International Academy of the History of Science