May 1877 Issue [Article] Popular exposition of some scientific experiments. Part III.–Things that are invisible.–The nature of sight.–Visual deceptions Download PDF Adjust Share by John William Draper, This article is only available as a PDF to subscribers. Download PDF Tags 19th century Fraunhofer lines Hallucinations and illusions Optical illusions Religion and science Research United States Vision More from John William Draper The national division The national division Franklin’s place in the science of the last century Adjust Share