Spine of Echinus Dr. Carpenter's Test for Flatness of Field -A Companion Slide to his Disc of Deal Test for Achromatism

摘要

Following my article on the "Disc of Deal, Dr. Carpenter's Test for Achromatism" in the Balsam Post and subsequently reprinted in this Journal [1 & 2] some interesting calls and correspondence were received including two requests from overseas. But it was a letter from Stanley Warren, of Edinburgh, that caused surprise.