54 J. D. Dana on the Homeomorphism of Mineral Species. 
4:3. This is the ratio between Chrysolite and Chrysoberyl. If 
119° 12’ in Chrysolite be perraistthe as corresponding to 119° 46! 
in Chrysobery!, then the macrodome of 64° — . Chrysolite, if 
referred to the form of Chrptohesth would be 
From Calamine to sapererie. the vertical axis is to that of the 
Barytes series nearly as 5 
In reviewing the acas « of Trimetric forms, the most promi- 
nent fact observed is the prevalent approximation in the values of — 
the angles of the unit prisms, to the three monometric angles, 
90°, 109° 28’, and 120°, or their supplements, 70° 32’, and 60°; 
above all, the angles approaching 109° 28’ and 70° 32’ ‘much pre- 
dominate. When the vertical prism is near 90°, domes neat 
109° 28’ and 70° 32’, characterize very many of the species; 
while domes near 120° belong to the rest of the species. And in 
the second great group, macrodomes near 70° 32’, and 109° 28; 
_ and brachydomes near 60° and 120°, determine the vertical an- 
gle of the prism, which i hcathes 101° 36’. Another large» 
group oie 120° and 60° as approximately the angles of the vel 
tical p 
The a that the axial ratios 1: 2 and 1: 3 are typical ' of 
certain groups has been mentioned. It is easy to make out, in 
many cases, simple ratios between the axes, or the sum of two 
of the axes and‘the third; but the importance that should be at 
tached to auch ratios is questionable. The following are a leW 
examples 
:b:¢ f ; 
Epistlbite (I= 100° 58’), 14065 "1: 12121 a+b=2e 
Calamine; ~- - - 17 1: £2766 Qa=e 
Brochantite, Se eS phd 1 : 1:2838 2a=c 
~ Cotun - + =~ - 05953:1:1:1868 = 2a=c 
Haidingetite, - - = 05945: 1: 1-1918 2a=¢ 
Géthite, - - - - - 06606:1:1-0888  3a=+¢ 
Polycrase, - - - - 1:0265:1:1:0913 2a=d+¢ 
Valentinite, - - - - 1:7934:1:1:2683. 2a=6+2¢ 
paps - - - 23408:1:12342 a=b+e 
(37), - - - 25606:1:12342 ta=b+e 
In Valentinite this relation is evidently dependent on the more 
authoritative and equally exact ratioa: b:ec=1: V4: V2 
‘any conclusions bearing on chemical formulas, and the chem 
ical relations of species, flow from the facts in the preceding. ee 
bles. But we leave, for the present, that branch of the 
without further remarks. 
* Since this paper was first printed, the author has found that M. 5 
Vierna recently pointed out similarities in the angles o' 
of 
Electric 
distinction 

pmo onan Gian ce, rile awl Cart . hag 9 Saget: Tanta ition od 3 
betwee’ St Lodoaoed 
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