Map of Heligoland, shewing the Island as it existed in the Seventh, Thirteenth, and Seventeenth Centuries / 
Mutlow, H.
[London :  Printed for T. Cadell and W. Davies, 
1819]
In: Travels in Various Countries of Europe, Asia and Africa. By Edward Daniel Clarke. Part the third, Scandinavia, section the first. p.8.