Vibrating Dams. 363 
sent peculiarities of structure which vary only in degree from 
those of the Labyrinthodonts, the existence in a fossil tooth of 
the Labyrinthodontic structure alone, would seem to be an insufli- 
cient character for determining to which of the two natural fami- 
lies, Sauroid fishes or Labyrinthodonts, it might belong. 'T’'hese 
remarks involve questions which we have no means at present of 
deciding, and would therefore submit them for the consideration 
of those favorably situated for instituting such comparisons as are 
necessary for arriving at correct conclusions. 
EXPLANATION OF THE PLATE. 
_ Fig. 1, transverse section of the tooth of Lepidosteus oryurus, 
Raf; a, pulp cavity; } and ¢, cementum; d, dentine; ¢, radia- 
tions from the pulp cavity ; f, tooth of natural size. 
. Fig. 2, highly magnified segment of preceding section; a, den- 
tine; b and c, cementum; d, one of the involutions of the camen- 
tum; é,. pulp. caVitYewnis eo) ge 
_. Fig. 3, calcigerous tubes highly magnified. 
_Fig. 4, portion of transverse. section of the tooth of the Lepi- 
dosteus platyrhinus, Raf.; a, ‘one of the radiations from the pulp 
cavity, bifurcated at its termination ; b, one of the processes from 
the cementum, having an undulated instead of a straight course 
as in the Lepidosteus oxyurus; ¢, dentine; d and, tooth aud 
transverse section of the natural size. 
ee ee 4 
Arr. XIV.—On Vibrating Dams ; by Etas Loomis, Professor 
‘of Mathematics and Natural Philosophy in Western Reserve 
P “College. j sigs ae Be gh ¢ | 
-Somerime in the winter of 1841-2, my opinion was asked re- 
specting a remarkable phenomenon noticed at. Cuyahoga Falls, a 
Village on the Cuyahoga River about eight miles from Hudson. 
The phenomenon consisted in the vibrations of the doors and 
windows, and other movable objects belonging to the buildings 
in the village. 'They were noticed at certain stages of the water, 
and‘at times ceased entirely. They were generally ascribed to 
a certain dam in the river; and various conjectures were formed 
as to the mode of their production. The subject was new to me, 
and I did not at first form any distinct idea of the phenomenon 
