Figure 78. — Brass surveying compass made by Benjamin Rittenhouse for Andrew 

 Ellicott and inscribed with both names. The instrument is described in Journal 

 of Andrew Ellicott (Philadelphia, 1803). USNM 310815. 



the estate of Mount Vernon, according to family manuscripts. It 

 was made by David Rittenhouse and presented by him to General 

 Washington, who subsequently gave it to Capt. Samuel Duvall. 



\ manuscript consisting of 14 letters relating to the surveying 

 compass is filed in the U.S. National Museum (USNM 92542). 

 The letters were written in 1851 and 1852 by George Washington 

 Parke Custis, Anthony Kimmel, and other Washington de- 

 scendants. 



Gift of Anthony Kimmel to the U.S. Government, and trans- 

 ferred to the U.S. National Museum in 1883. USNM 92538. 



Figure 79. 



Zenith Sector for measuring the angle between a star at its zenith 

 and the vertical. Made of brass, with focal length of 6 ft. and an 

 aperture of 2/2 in. The original lens was made in London about 

 1780. The instrument was made in the old pattern with brass 

 tube and mountings and a wooden supporting post. The tube is 

 suspended by trunnions at the top and swings against a graduated 

 arc extending north and south for measuring zenith distances in 

 the meridian. It is adjusted in the vertical by a plumb line whose 

 errors are eliminated by reversing the whole mounting about the 

 supporting post. Constructed principally by David Rittenhouse, 

 with some modifications by Andrew Ellicott. 



144 



