According to Guinness World Records Vatnajökull is the object of the world's longest sight line, 550 km from Slættaratindur, the highest mountain in the Faroe Islands. GWR state that "owing to the light bending effects of atmospheric refraction, Vatnajökull (2119m), Iceland, can sometimes be seen from the Faroe Islands, 340 miles (550 km) away". This may be based on a claimed sighting by a British sailor in 1939. The validity of this record is analysed/undermined in mathematical and atmospheric detail by J.C. de Ferranti 