522 



WRIGHT! PRECISION PROJECTION PLOT 



the purpose better, as the observer could draw on it only those 



lines which he needed in his triangles. 



In 1885 Commander C. D. Sigsbee 2 published a paper on 



Graphical Methods for Navigators in which was included an 



exceedingly exact 

 stereographic projec- 

 tion net 18 inches in 

 diameter. The great 

 and small circles are 

 drawn at 1° intervals 

 on this net, which is 

 the most accurate in 

 existence. This net 

 was issued as a sepa- 

 rate sheet in 1888 by 

 the U. S. Hydro- 

 graphic Office. 3 Solu- 

 tions with it were 

 made commonly on a 

 sheet of tracing paper 

 placed above the net 

 and rotated about the 

 center point. Experi- 

 ence has shown 

 that projection nets 

 printed on paper suf- 

 fer distortion as a re- 

 sult of the unequal 

 contraction of the pa- 

 per on drying. To 

 obviate this difficulty, 

 which may become 



Fig. 1. Precision projection plot and stand. 



2 Proc. U. S. Naval Institute, 11: 241-263. 1885. 



3 Graphical Solution of Spherical Triangles. By Commander C. D. Sigsbee, 

 U.S.N. Published December, 1888. U. S. Hydrographic Office. Plate 513. 

 Price 40 cents. Republished in 1896 in Sigsbee's Graphical Methods for Navi- 

 gators. U. S. Hydrographic Office. 



