Description

An important Hadley-type quadrant in mahogany wood with bone scale and name plate c.1790.

Made during the first year of the partnership of Gilbert, Wright & Hooke at the Navigation Warehouse, 148 Leadenhall St., London,  this instrument has many nuances not seen before or after. Having a 17 inch index arm radius and a 15 inch arc circle, it is a rare survivor in near perfect condition. The mahogany frame has a rich colour and the brass has taken on a good patination. Once belonging to Capt. ? John Holdsworth, it is dated 1791. 

In addition, the scale runs out to 90-95 degrees and is engine/hand? divided by G.N. (with fouled anchor). I believe G.N. was George Newman (w. 1769-1808). The scale is subdivided by degrees in blocks of 5 and then further subdivided by thirds (20 minutes). The vernier reads from 0-20 in 0.1 degree (1 minute) increments making this a very accurate instrument for it’s day. Later quadrants (reflecting octants) had verniers that ran from 0-10/15 in both directions (engine divided by S,B,R) as they had permanent peep sights fore and aft (this instrument has only one). The vernier/index arm runs along the arc circle smoothly yet with resistance by an odd brass semi-circle behind. There never was a locking nut for the arm , as seen in later instruments.

Although the primary mirror has been replaced, the others are intact and usable as most of the silvering still exists. The three interchangeable coloured light filters are intact. The peep sight can be removed and used for back sighting, although this was a fairly new concept which relied on other instruments of navigation to read both horizons for Sun and Moon or artificial horizons of mercury. The secondary mirrors are adjustable from the rear by wings nuts and brackets (never touched).

The only other fault of the instrument is a small missing piece of the vernier scale although the demarcations lines are still there, to be read i.e.  1/20 degrees 1-3 and the rectangular bone plate is missing from the back side (does not detract).  The instrument can sit on it’s three bun feet or hang on a wall (previous owner had a piece of copper wire on upper foot for this reason). There is no case/box. No chips or cracks. The photos do NOT do it justice.

The newly formed and ever changing partnerships of William Gilbert is hard to follow and there must have been some personality/money/expansion issues surrounding this chap. Many of these instrument makers worked/played at the navigation warehouse and alliances were seemingly common among artisans and apprentices. William Gilbert came from a long line of instrument makers, most successful but it seems he struggled. Partnerships with Wright, Hooke and many others would make him a bit of a “loose cannon”. This three way partnership not only dates the instrument but also makes it quite the rarity as it only lasted 10 years (better than the track record of Gilbert & Wright which was only 1-2 years before bringing in Hooke). Later Gilbert teamed up with his son(s) and it finally became Gilbert & Co.  Questions and comments welcome.