106 Editorial Note. 
Tin is in section I; rutile, cassiterite, etc., in section IT; raga 
etc., in section ; anatase, etc., in section IV. say, on 
page 196, that these sections Lil, Thy 2, isnetivite 4 a single 
group; and that in this group “the basal angle of the fundamental 
this 
octahedron is near 90° ;” and this group, which includes Anatase, 
I name the Rutile group. “This j is in direct opposition to the state- 
ment of my views by Prof. Hinrichs. 
Brookite (of the orthorhombic system) I do not compare directly 
with rutile. ire : lustrate on pages 200 and 202 the near rela- 
tions of its prismatic form to the tesseral system. I have not re- 
Brot Hi drreceotibed, Vike that of brookite, as so little iipobian as 
of. Hinrichs does; andI do not yet see reason to change my opin- 
ion on the subject. 
With regard to Chrysoberyl, I point out similar relations to the 
tesseral or isometric system. A table on page 201 contains ortho- 
rhombic species in which the vertical prism is near 120°. this 
table, and the same section of it, occur chrysoberyl, aragonite, dis- 
crasite, and a number of other species. In the remarks which fol- 
ow on the tesseral relations of the forms, I ee went that in this 
ag the peu soms is were 109° 28’, the angle of the octahe- 
dron. Mor over, in order to bring out this sist ae I have taken 
ios: mene sea the symbols af and #4 stand before the values of the 
‘angles of the domes of chrysoberyl in the table. The query natu- 
rally arises whether Prof. Hinrichs had not seen ai oe Dana’s Min- 
eralogy, and the ¢esseral relation explained to his h 
Prof. Hinrichs is wrong in making the formula = ree of 
oo bane a protoxyd) Be 4i, or that of the Spinel group. 
Be®tAl. 
An $2 ase Fd the “ Atom Mechanics,” Prof. Hinrichs has the follow- 
ae or antimonial silver, has according to Dana, the verti- 
cal prism 1 19° 59’; ; deviating therefore only about 1 minute from the 
hexagonal. And ‘hia, notwithstanding the admission of many de- 
grees of variation in the hexagonal system (in relation to the ver- 
tical axis) without destroying the isomorphism! A deviation in 
another . however, even so slight as this, is followed by 
complete exclusio 
The point sacl is this: that I refer discrasite to the orthorhombic 
rather than hexagonal system, when there is a deviation of only 
$ geometrically orthorhombic, as distinctly so = any other 
mbio tae The question n of relation to the hexeaene 
system is not one to be considered in such a reference, F 
not a has has “Dana” done this, but so have al] other ken a 
not onl bees: ct but also in the whole symmetry of the erys- 
tten on the Subject ageath thes iN as to any iso- 
hexagonal 
a Bo relations with the 
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