Hagioscope
HAGIOSCOPE (from Gr. 07105, holy, and aKmtiv, to see), in architecture, an opening through the wall of a church in an oblique direction, to enable the worshippers in the transepts or other parts of the church, from which the altar was not visible, to see the elevation of the Host. As a rule these hagioscopes, or " squints " as they are sometimes called, are found on one or both sides of the chancel arch. In some cases a series of openings has been cut in the walls in an oblique line to enable a person standing in the porch (as in Bridgewater church, Somerset) to see the altar; in this case and in other instances such openings were sometimes provided for an attendant, who had to ring the Sanctus bell when the Host was elevated. Though rarely met with on the continent of Europe, there are occasions where they are found, so as to enable a monk in one of the vestries to follow the service and communicate with the bell-ringers.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)
