Elkin, with the Yale heliometer, obtained 0.032 of a second of arc.
"The New Heavens" by George Ellery Hale
Fraunhofer, moreover, constructed for the observatory at Koenigsberg the first really available heliometer.
"A Popular History of Astronomy During the Nineteenth Century" by Agnes M. (Agnes Mary) Clerke
He also invented a heliometer, afterwards perfected by Fraunhofer.
"Encyclopaedia Britannica, 11th Edition, Volume 4, Slice 3" by Various
They are obtained from late improved measures of the velocity of light, and from measures by the heliometer.
"Scientific American Supplement, No. 648, June 2, 1888." by Various
Nor is it difficult to imagine the probable course of reasoning which led Bessel to select the model of his new heliometer.
"Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 2" by Various
Bessel, meanwhile, studied 61 Cygni with a Fraunhofer Heliometer in Königsberg, using two nearby companions.
Astrometry during the past 2000 years