1720 Hasebroek cross-staff (reproduction)After finishing the Davis quadrant reproduction I wanted to reconstruct an even older navigational instrument: the cross-staff. I decided to go for a reproduction of the 1720 Jochem Hasebroek Cross-staff as its dimensions where not too large, so getting the correct wood in it's right dimensions should not pose any problems. Another reason to go for a late cross-staff was that I wanted to create a staff with all the possible 'options' available (4 vanes, altitude and zenith graduations and brass aperture discs, although the latter were not found with the original instrument).
I started working on this staff in January 2004 and finished it by the end of March. Materials used on this reproduction are ebony for the staff, pear wood for the vanes, cow bone (part of the shoulder blade) for the horizon bone or 'beentje' as it was named, and brass for all metal parts.
The first description of the baculus Jacob dates back to 1342 (Levi ben Gerson [1288-1344]) and it was introduced at sea by the Portuguese around 1515. This type of instrument was the forerunner of many different staffs of which the Davis quadrant reproduction is the most famous.
Early cross-staffs (cross-staves) was used facing the sun and therefore required the navigator to look straight into the bright sunlight. Thomas Hood invented the shadow casting method, which lead to the principle of backstaff instruments by Thomas Hariot. These backstaffs (or back staves) were instruments that allowed to measure the sun's altitude by casting the shadow of a shadow vane, while standing with ones back towards the sun, a big advantage over the cross-staff. For this reason the cross-staff was also sometimes referred to as the fore-staff. Examples of backstaffs are the demi-cross, hoekboog and Davis quadrant.
After the introduction of the back-staff the cross-staff was also used in a backwards fashion, casting the shadow of one of the vanes on a bone that was attached to the smallest vane. In the middle of the 17th century the brass aperture disc was invented, a clamp that fitted to the end of the larger vane, hugely improving the quality of the backwards observation. Initially only one brass aperture disc was used, but by the end of the 17th century two were in fashion; one for casting a beam of light and one as a visor. Both the cross-staff and the back-staff were used until the introduction of the octant1.
If you have any questions and/or remarks please let me know.
1580s Mariner's astrolabe 1590 Hood's cross-staff 1618 Demi-cross 1623 hoekboog 1660 spiegelboog 1661 Kronan cross-staff 1720 Hasebroek cross-staff 1734 Davis quadrant Early 19th c. ebony octant Late 19th c brass octant 1941 U.S. Navy quintant Hirado navigation set