JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VI SEPTEMBER 19, 1916 No. 15 



MATHEMATICS. — A precision projection plot. F. E. Wright, 

 Geophysical Laboratory. 



For the solution of spherical triangles and of certain crystal- 

 lographic-optical problems graphical methods are often used. 

 These problems involve the angular relations between direc- 

 tions in space and are best presented and solved by means 

 either of a sphere or of some projection of the sphere such as the 

 stereographic projection. The first stereographic projection plot 

 or net of which the writer has found record was published in 

 1854 as "The Great Circle Protractor" by Prof. W.Chauvenet 1 

 of the U. S. Naval Academy in Annapolis, Md., and was in- 

 tended for use by navigators in great circle sailing and in the 

 solution of spherical triangles. This chart consists of an equa- 

 torial stereographic projection net, 15 inches in diameter and with 

 parallels and meridians 1° apart. A second and similar plot 

 printed on transparent material was placed above the first net 

 on a pivot and could be rotated about the common center. 

 The maze of lines hereby introduced rendered, however, the 

 application of the projection difficult and the method was not 

 used to any great extent ; it was found that tracing paper served 



1 First described in May, 1854, at the Washington meeting of the American 

 Association for the Advancement of Science. It was adopted the same year by 

 the U. S. Navy Department and the TJ. S. Naval Academy; was reissued in 1867 

 by the U. S. Hydrographic Office. Described also in Great Circle Sailing, by 

 G. W. Littlehales. TJ. S. Hydrographic Office, No. 90, 1889; see also S. L. Pen- 

 field, Am. J. Sci. (4), 13: 250. 1902. 



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