30 



CALIFORNIA ACADEMY OF SCIENCES. 



Compaiing von Kath's calculated angles and mine with the 

 mean values, it will be found that for two thirds of those given 

 by von Ratb, my values are nearer, and for one third his are 

 nearer the mean value observed. It will be noticed that of 

 his fundamental angles, two (s : s and c : m) are extremes 

 among all thus far observed, while his third angle (g : c) agrees 

 exactly with my calculated value of g : c = 153 4' 3". 



I did not include the angles observed by Prof, von Rath in 

 making up the mean values given in my table, as I was uncertain 

 about their fulfilling the conditions I had set for securing great 

 accuracy in all angles entering into the mean values. 



Prof, von Rath speaks once more in his letter, concerning the 

 general resemblance between colemanite and datholite, which 

 he considers very striking 



