Letter from George E [Ellery] Hale, Carnegie Institution of Washington, Mount Wilson Solar Observatory, Pasadena, California, to Sir Joseph Larmor, St. John's College, Cambridge, England He sent Larmor a stereogram on glass a few weeks ago, showing hydrogen flocculi surrounding a group of sunspots on 7 Augusy 1915. He should have added the following memorandum regarding the stereoscopic effect. It is easily shown that the angular value of separation of the images necessary for stereo vision is exceeded by the displacement due to solar rotation between the exposures. In all three forms of spurious effects are present, which he lists and explains. As a check on the reality of the stereoscopic effect, photographs have been made of a globe with roughened surface, turned, and enlarged by magnification, all corresponding to the solar photographs. 19 January 1916