244 J. D. Dana on the Tsomorphism and 
ous; and also the more general law,—Unlike compounds, of the 
same or different elements, may be isomorphous, and when so, 
they are alike or proportional in atomic volume. 
. Cleavage may differ among substances, and yet the species 
be isomorphous. Thus angite and hornblende have different 
cleavage; anatase and horn quicksilver; sulphur and scorodite. 
This is a point, however, which requires much more investigation. 
II. The relations of atomic volume shown in the three columns 
are all of interest, but especially those in the third or C column. 
The C relation is seen to be in general a relation of approximate 
equality, while the A relation when simple is usually one of mul- 
tiple ratio; and sometimes it is far from simple. The C relation 
exhibits the comparative character of the monoclinic, triclinic and 
monometric feldspars, in a simple and obvious manner, while from 
the A relation, no deduction could be made: and so in other 
cases where general principles are concerned. The C relations 
often show a consistent difference between a substance with its 
allies and others unlike, when no such difference is apparent in 
the A relations. The C relation moreover exhibits the differences 
which are compatible with a ratio of equality, and hence enables 
us to compare more correctly the A relations. It is unnecessary 
to review here the ratios in the C column. We mention only a 
few cases of the ratios (approximate) apparent in the A column 
which in many cases are simple and deserve full consideration. 
We take the number for the species first mentioned in each para- 
graph as the unit for comparison with the others. 
1, Pyroxene, dif. var., 1; acmite 14; hornblende 1}; borax 2; glauber salt 2. 
2. Epidote 1; zoisite 1; Ural orthite 14; Hitteroe orthite 4. 
8. Orthoclase 1; ryacolite %; loxoclase 2; baulite 14; albite 1; labradorite t; 
anorthite 1}; vosgite 14; andesine 1}; petalite 44. 
4, Kyanite 1; bucholzite 74,2; ; sillimanite (one var.) 24. 
5. Quartz 1; chabazite 20. In deducing the ratio here as in other cases, we have 
some reference necessarily to the difference observed in the C ratios. 
6. Talc, 1st var, 1; 2d var. 1}; 8d var. soy. In the C column the numbers are 
nearly equal. 
_7. Chrysolite 1; chrysoberyl 4 (or 1); villarsite 4°6 ; serpentine 5; Epsom salt 2; 
picrosmine 34, 
8. Rutile 1; zircon 3—9. Scheelite 1; fergusonite 3. 
We do not pursue this further, as the ratios are readily deduci- 
ble from the table. 
IV. The view of Scheerer, that three of water may replace 
one of magnesia, if true, is only true for a special case or set of 
eases, and is subordinate to the more general law of atomic vol- 
ume. If true, we should expect, in dividing the aggregate atomic 
volume by the number of atoms of the elements, that it wou 
be right to reckon three atoms of water as eqivalent to one of 
magnesia, instead of counting each element as equal to one ; but 
the facts observed are opposed to this course. 
iby 
pee i 
sign Saeie 
