HELIOSCOPE, in optics, a ſort of telescope, peculiarly fitted for viewing the ſun, without hurting the eyes. See TELESCOPE.
As the ſun may be viewed through coloured glaſſes, without hurt to the eyes, if the object and eye glaſſes of a telescope be made of coloured glaſſ, as red or green, ſuch a telescope will become an helioscope.
But Mr Huygens only uſed a plain glaſs, blacked at the flame of a candle on one ſide, and placed between the eye-glaſs and the eye; which anſwers the deſign of an helioscope very well.