In May of 1803, a procurement receipt documents purchases for the Lewis & Clark expedition from the shop of Philadelphia Mathematical instrument make Thomas Whitney. In use, this vernier or Rittenhouse type compass was mounted on a staff with a ball & socket leveling device at the top. It was used to run compass and chain courses up tributaries and to record other land features. This compass is signed, "Tho. Whitney, Maker. Philadelphia." and dates circa 1799-1803.  (Actually it is Thos.cs)

Both the octant and the sextant are recognized more for navigation at sea rather than surveying on land. However, both instruments were used extensively during 18th and 19th century exploration surveys for both horizontal triangulation and for equal altitude readings for finding latitude. This ivory and brass octant dates circa 1800 and is with backsights and two positions for the shade filters.

The brass sextant was a more refined instrument, with optional filters and sighting telescopes and a more accurately divided arc and vernier. In use, several celestial readings were averaged for "mean" angle. This sextant dates from the 1st quarter of the 19th century. Both the Octant and this Sextant are typical of those used during the time Lewis & Clark were active

Both the octant and the sextant were dependent upon a fixed horizon in order to record accurate readings. Without the use of a horizon at sea, the artificial horizon was employed to offer a level reflective surface. In use, mercury or water was placed in the trough. The liquid would reflect the star and the instrument could then obtain a double angle of the altitude. The glass hood was used to shield the liquid from wind. This period cased Artificial Horizon is signed, "Troughton & Simms London." It includes the cast iron tray, mercury bottle, funnel and glazed hood.

Once readings were recorded and noted, they were then plotted on maps. This plotting, or mathematical instrument drawing set includes an ivory ruler, pens, parallel rule, and a crude protractor, and a sector rule used for trigonometric computations, all within the original shark skin case. More accurate plotting of angles was made with the use of a vernier protractor. This circa 1810 geared vernier protractor is signed, "Gilkerson & Co. Tower Hill London."

In May of 1803, a procurement receipt documents purchases for the Lewis & Clark expedition from the shop of Philadelphia Mathematical instrument make Thomas Whitney. In use, this vernier or Rittenhouse type compass was mounted on a staff with a ball & socket leveling device at the top. It was used to run compass and chain courses up tributaries and to record other land features. This compass is signed, "Tho. Whitney, Maker. Philadelphia." and dates circa 1799-1803. -- (Actually it is Thos.cs)

Both the octant and the sextant are recognized more for navigation at sea rather than surveying on land. However, both instruments were used extensively during 18th and 19th century exploration surveys for both horizontal triangulation and for equal altitude readings for finding latitude. This ivory and brass octant dates circa 1800 and is with backsights and two positions for the shade filters.