WRIGHT: PRECISION PROJECTION PLOT 523 



serious when accurate measurements are to be made, R. A. 

 Harris 4 suggested that a polar stereographic net be drawn 

 over the Sigsbee equatorial net, so that all rotations can be 

 accomplished directly in the projection itself and the errors due 

 to distortion after printing be thus eliminated. 



Stereographic projection nets were made use of by Fedorow 5 

 and Michel Levy 6 for the representation of the optical data of 

 the plagioclase feldspars. In 1901 Penfield 7 published an ex- 

 tended account of the stereographic projection and described 

 several protractors to facilitate its practical application. In 1902 

 G. Wulff s published a stereographic net and claimed to intro- 

 duce new and improved methods of using the stereographic pro- 

 jection; his method is commonly referred to in the literature as 

 Wulff's method. It is of interest to note, however, that both 

 Chauvenet and Sigsbee had published stereographic projection 

 nets many years before Wulff and that their nets were of greatly 

 superior precision. In view of the fact that the new method 

 described by Wulff is identical with that which Sigsbee described 

 many years before, it is incorrect to name the method after Wulff; 

 if the method is to be called after its first originators it should 

 be named the Chauvenet-Sigsbee method. 



In 1906 G. W. Littlehales 9 published an atlas of many plates 

 of a carefully drawn stereographic projection net 12 feet in 

 diameter. By use of this net spherical triangles can be solved 

 with an error of only 2' in favorable cases. 



Improvements in the method of mounting and rotating the 

 projection paper were suggested by Wulfing, 10 Johannsen, 11 

 Wright, 12 and Noll. 13 



4 G. W. Littlehales. Great circle sailing. 2d edition. U. S. Hydrographic 

 Office, No. 90: 41-45. 1899. 



5 Zeitschr. Krist,, 21: 574-714. 1893: 22: 229-268. 1894; 26: 225. 1896; 27: 

 337. 1897; 29: 604. 1898. 



6 La Determination des Feldspaths. I, Paris, 1894; II, Paris, 1896. 



7 Am. J. Sci. (4), 11: 1-24, 115-114. 1901; 13: 245-275, 347-376. 1902; 14: 

 241-284. 1902. 



8 Zeitschrift f. Kristallographie, 36: 14. 1902. 



9 Altitude, azimuth, and geographic position. Philadelphia, 1906. 

 10 Centralblatt ftir Mineralogie, 1911. 

 "Journ. Geology, 19: 752. 1911. 



12 Carnegie Institution of Washington Publication 167: 166. 1911. 



13 Centralblatt ftir Mineralogie, 380, 1912. 



