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WRIGHT: TRIGONOMETRIC COMPUTER 



crystal angles with temperature the position of each crystal face 

 is determined on the two-circle goniometer by means of two 

 angles (polar distance and azimuth). Having given the posi- 

 tion-angles of any two faces, the angle between them can be 

 found by the solution of a spherical triangle. 



Fig. I. Photograph of trigonometric computer. 



In 1913 the writer had occasion to solve many triangles of this 

 type, and to save time had a mechanical computer constructed 

 in the instrument shop of the Geophysical Laboratory. This 

 instrument has proved to be satisfactory in practice for the 

 solution of oblique spherical triangles in which three of the angles 

 are given and the value of any one of the three remaining angles 

 is sought with a precision of about half a minute. The computer 

 was designed for, and functions best in, the solution of the 



