212 A TREATISE ON NEW PHILOSOPHICAL INSTRUMENTS, FOR VARIOUS PURPOSES IN THE ARTS AND SCIENCES. WITH EXPERIMENTS ON LIGHT AND COLOURS. BY DAVID BREWSTER, LL.D. FELLOW OF THE ROYAL SOCIETY OF EDINBURGH, AND OF SCOTLAND. La revolution que nous demandons ne peut avoir lieu que dans les BAILLY ΤΟ 4 JOHN PLAYFAIR, Esq. PROFESSOR OF NATURAL PHILOSOPHY IN THE UNIVERSITY OF EDINBURGH, FELLOW OF THE ROYAL SOCIETY OF LONDON, AND SECRETARY TO THE ROYAL SOCIETY OF EDINBURGH. IN dedicating to you this volume, I discharge a duty, which both Friendship and Science impose upon me. The kind approbation which you formerly bestowed on some of the Instruments described in the following pages, was the strongest excitement to my earliest exertions; and the constant interest you have since taken in the progress of my researches, has often encouraged me to pursue them under circumstances not very favourable to physical investigations. I shall ever regard it as the most fortunate event of my life, that I have shared so |