Influence of Pressure on the Density of Liquids. A9 
Hab. Trunks of trees and old rails; New England. The 
Cetraria lacunosa of Acharius, was a lichen discovered by the 
late Mr. Menzies, on the North West Coast. Having received 
from that venerable botanist a specimen of his plant, I find it is 
quite distinct from what has commonly passed for it here. 'The 
plant of Menzies and Acharius is well represented in the figure 
given of it by the latter author, in his Methodus. ‘The thallus 
is broad and expanded, very deeply cellulose and reticulate, and 
very rigid; the apothecia large. Ours is noticeable for its com- 
plicated ascending lobes, which are crisped and beset with black 
grains at the margins, the apothecia becoming at length perforate. 
It has several points of resemblance to C. ciliaris, its constant 
companion, and also a lichen peculiar to this continent, but can- 
not be confounded with that species, which is always remarkable 
for its dark brown or bronze hue, and much shorter laciniz. The 
under surface is most commonly white in the specimens of our 
plant, but I believe this is an accidental and atypical state. 
Sotorina saccara, (Ach.): thallo membranaceo appresso lobato 
cinereo-virescente lobis obtusis, subtus albo avenio fibrilloso, 
apotheciis lamine frondis primum applanatis mox saccato-depres- 
sis nigro-fuscis. DC., Fries, Lichenogr. p. 49. 
Hab. Trenton, N. Y., Mr. Greene. This curious genus is new 
to the United States; and the species has not before been pub- 
lished as American. 'The plant is distinguishable by its rounded 
black apothecia, more or less sunk in the surface of the cinereous- 
virescent thallus. 
Art. V.—Remarkable example of the Force of Expansion and 
Contraction, exerted by bodies when subjected to alternations of 
Temperature,—with a reference to the question whether the 
Jreezing point of liquids is influenced by differences in pres- 
sure; by Lewis C. Breck, M. D., Professor of Chemistry, é&c. 
in Rutgers College, N. J. 
TO PROFESSOR SILLIMAN, 
At one of the docks in the city of New York, ships are raised 
from the water, for the purpose of being repaired, by hydraulic 
presses consisting of cylinders with pistons or rams, having cross 
bars or arms at the ends. ‘'T’o these arms are attached the iron 
Vol. xtv, No. 1.—April-June, 1843. 7 
