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PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. 59. 



ured by the newer instrument. The numerous calculations of angles 

 given in the tables were made by the use of Goldschmidt's formulas 

 and the crystal drawings, which had been made by older methods 

 using axial crosses, were redrawn, for the sake of the greater accu- 

 racy attainable, from the gnomonic projection. It was possible with 

 the 2-circle goniometer to measure many faces which it was practically 

 impossible to measure zonally. It may be appropriate to state that 



Figs. 3-4.-3, Orthographic and clinographic projections showing a crystal of type 1, this 

 being the development of most frequent occurrence at westfield. 4, orthographic and 

 clinographic projections of crystal 2, prismatic by elongation on the o axis. 



the writer, who up to this time had used only the 1-circle goniometer 

 and attendant methods of plotting, projection, calculation, and 

 drawing, is thoroughly convinced of the incomparable superiority of 

 the 2-circle goniometer and the methods devised to accompany its use. 

 It is necessary in measuring these datolites to handle on the goni- 

 ometer some large and decidedly awkward crystals, since many of the 

 rarer forms are practically confined to the largest crystals. The 



