J. D. Dana’s Mineralogical Contributions. 249 
vibrations would be a very ingenious mechanism for gravitation, 
if the Newtonian law could be deduced in a tolerably simple 
manner from it, but this requisite seems to throw us back on the 
strange theory of a universal coexistence of all matter. Its in- 
aptness for illustrating molecular mechanics is peculiarly striking 
if we attempt to imagine ray vibrations for the several phases o 
molecular constitution. In fact, the reduction of all forces to one 
law, such as that of Boscovich or Faraday, is like describing all 
animals as of the color of a chameleon. 
In strange contrast with the Theoria and the Speculation, is 
. the investigation by Mossotti, which is based on real mechanical 
principles, and which, though quite imperfect, leads to real re- 
sults. By assigning definite size to atoms, and applying the sim- 
ple Newtonian law of force to two kinds of matter, conditioned 
as in the Franklinian electrical theory, modified by Epinus, Mos- 
sotti has avoided most of the objections urged against the theory 
of spheres of force, and has given a glimpse at least of what heat 
'1n the constitution of masses. By extending his investigation, 
and by supplying some deficient elements, molecular mechanics 
may at last be established on that simple and sure basis of ordi- 
nary mechanical principles, which Newton and Laplace have so 
distinctly foreshadowed, and which the expanding realms of 
Physical science demand with a positiveness hitherto unknown. 

Arr, XX XI.— Contributions to Mineralogy ; by James D. Dana. 
l. On the relation of Leadhillite in crystallization, to the Anhy- 
drous Sulphates and Carbonates. 
HE sulphato-carbonate, Leadhillite, shown to be trimetric in 
“rystallization by Brooke and Miller, has three prominent points of 
Interest: its approximation in form, viewed in one direction, to a 
‘egular hexagonal prism—its hemihedrism, which gives it a mono- 


clini nee 
bane aspect—its twin-composition, under which it takes a rhom- 
‘ edral character, Figure 1 represents the known planes, taken 
“on Senizs, Vol. XVIII, No. 53.—Sept, 1854. 32 
