In facsimile, a frequency modulationsystem where one frequency represents picture black and another frequency represents picture white[?]. Frequencies between these two limits may represent shades of gray
An intentional frequency change used for modulation purposes
... St. Ives, Cornwall
Penlee House, Penzance[?]
Tate St. Ives[?]
Cumbria
Abbot Hall Art Gallery[?], Kendal[?]
Beatrix Potter Gallery[?], Hawkshead[?]
Cumberland ...