112 



Type 1. Type 3. 



at 50° 2-763 2-739 



- 60° 2-762 2-739 



- 70° 2-761 2-739. 



By this table it is seen that type 1, which does not alter 

 its crystalline form until ca. 120°, keeps its specific gravity all 

 but unaltered by a heating to 70°, while type 3 suffers a very 

 distinct diminuation in specific gravity below 40°, that is to say, 

 exactly at the same time, as it becomes hexagonal. From this 

 it is clear that an alteration of the topical axes must take place 

 at the transformation, but how this alteration takes place in 

 details cannot be said as long as we have no corresponding 

 measurements of angles. 



The difference between the two types pointed out above 

 may be illustrated, when a crystal of each type is selected with 

 exactly the same specific gravity; I succeeded in finding two 

 crystals, wich floated at the same time in the fluid at 50°; 

 when the crystal of type I was made to float after the cooling, 

 the crystal of type 3 at the same time sank to the bottom. 



The optical axial angle is stated somewhat differently; 

 Brøgger has 



2E = с 60° 

 for the Norwegian catapleiite; Flink has, for the Greenland 

 mineral of type 3 



2E = 30°. 



The material brought home by Bernbcrg's expeditions is 

 distinguished , more than any other Greenland form of the 

 mineral, by possessing large homogeneous parts in the interior 

 of the crystals; in such crystals I have found directly by 

 reading of the micrometer 



2Æ = 42°. 



By measuring in glass hemispheres with an index of re- 

 fraction of 1-53 has been found for yellow light 



2 Я = 26^2° 



