Original covers lost, now bound in paper, probably later in the 18th century. First page bears the stamp of University Library, Cambridge.
A pamphlet published no doubt to be presented to the Board of Longitude in an attempt to win the £20,000 prize.
The first part of the pamphlet concerns a type of quadrant invented by Rowe.
The second part, pp. 13-47 is an "Essay on the Discovery of the Longitude, By a New Invention of an Everlasting Horometer: Founded on the most Unerring Principles of Nature."