Scheiner's helioscope, after a drawing in in Scheiner's Rosa Ursina , reproduced from The history of the discovery of the solar spots , in Popular Astronomy , 24 , W.M. Mitchell, 1916.
While Galileo largely abandoned systematic sunspot observations following the publication of his Three letters on Solar Spots , Scheiner devoted himself fully to sunspot observations. He improved on the projection method of Galileo and Castelli by designing a specialized telescopic solar projection instrument, which he called heliotropii telioscopici (helioscope being a rough contracted translation). This represent the earliest known equatorially mounted instrument.
-Written and last revised 29 December 1997 by paulchar@ucar.edu.