Description
In November 1944, R.S. Whipple’s donation to the University of Cambridge was put on show in the East Rooms of the Old Schools. The University accepted the donation on the condition that they found a new institution within which to house the collection.

Whipple himself wrote a guidebook to this exhibition, describing some of the more important objects and books on show. The front cover includes the following declaration: “The Exhibits are drawn from the Collection which Mr R.S. Whipple is presenting to the University and will form a nucleus for a History of Science Museum and Library in Cambridge.”

Whipple's explanatory text for this backstaff (and for Wh.0685) was:

"Back-staffs. This instrument was invented by John Davis about 1540 for the observation of the sun's altitude at sea without the necessity of looking directly at the sun. Two instruments, c.1700, are shown."
17/10/2025
Created by: Hannah Price on 17/10/2025

Description
The backstaff is a navigational instrument used to find latitude. It was introduced during the 17th century as a replacement for the crosstaff. With a crosstaff the Ship’s navigator would have to look directly into the sun which was often to bright. To use the backstaff the navigator was able to stand with their back to the sun and use the shadows cast on the instrument to take readings.

To use the backstaff the backsight and the horizon slit are lined up. The shadow vane on the small arc is moved until its shadow falls onto the horizon slit. The combined angle of the backsight and the shadow vane gives the angle of the sun and therefore the latitude.

The backstaff has a standard pattern of 2 main “limbs”, in ebony rosewood, pear wood or mahogany with the arcs and occasionally the braces in boxwood.

The backstaff was replaced by the octant which began to be made commercially from the mid 18th Century. Unlike the backstaff the octant was not affected by the movement of the ship when the navigator attempted to take readings.

Both the octant and backstaff continued to be produced and used into the 19th Century despite competition from the more accurate and versatile sextant. This may be because these instruments were cheaper and more affordable than the sextant.