Telescopes. Primary Documentation, you can't beat it.

So it seems that small telescopes were used in the mid 18th century, even though this person appears to be looking through his telescope backwards !

Drawing of a sailor, Louis Philippe Boitard, mid-18th Century, British Museum.

The author's replica telescope with a crude leather wrap & leather carry pouch.

The Georgian Age-At Sea.

Diary Of An 18th Century Sailor.

http://www.dailymail.co.uk/news/article-1044940/Diary-18th-century-sailor-provides-fascinating-insight-life-decks-Nelsons-navy.html

Alexander Selkirk's survival on Juan Fernandez Island 1704-1709.

The story of Robinson Crusoe written by Daniel Defoe, is believed to have been inspired by the survival story of Alexander Selkirk. Here is the list of items he was left with when abandoned on Juan Fernandez Island in 1709.

Author's Note: Does anyone know what an 18th century "flip-can" is?