156 PROCEEDINGS OF THE AMERICAN ACADEMY 



Zone [010, 110] (110) A (010) = 65° 33' 



(010) A (110) = 65° 44' 

 (TIO) A (TTO) = 48° 28' 

 (TTO)A(OTO) = 65° 521' 

 (OTO)A(ITO) = 65° 35' 

 (ITO)A(IIO) = 48° 44' 

 359° 56^' 



Zone [010, Oil] (010) A (021) = 44° 41' 

 (021) A (Oil) = 18° 30' 

 (Oll)A(OTl) = 54° 5' 

 (0T1)A(0T0) = 62° 56' 



63° 11' 



180° 12' 



(ITO)A(OII) = 122° 321' 

 (Oil) A (110) = 57° 18|' 

 179° 51' 

 (0T1)A(TT0)= 57° 21' 



The crystal face (OTl) was somewhat imperfect, so that the reflected 

 image was extended in width. Hence, the angles between (Oil) and 

 adjacent planes are rendered uncertain, but only by the small value 

 of 7' or 8'. All the other faces gave exceedingly sharp reflections. 



From these considerations upon the system in which tribromacrylic 

 acid crystallizes, it will appear that we have to deal with a question 

 of small differences, and that in consequence of the very prominent 

 monoclinic habit, we are justified in making these crystals monocliuic, 

 and not triclinic, as Becke has determined them. 



