366 Vibrating Dams. 
Il. Dam in East Windsor, Conn. 
The following information is derived from a letter from Mr. 
M. W. Osborn, dated Florence, Erie Co. Ohio; and another from 
Mr. N. 8. Osborn, dated Scantic, Conn. This dam ison the 
Scantic River, in the township of East Windsor. It was formerly 
eighty feet in length; but is now one hundred, and is perfectly 
straight. It is based on a sandstone rock, raised from six to 
seven feet from the rock, and about five feet from the surface of 
the water below the dam. The dam is a flat one, the rafters be- 
ing raised not more than twenty five degrees. It was built by 
raising two tiers of, logs, one in front and the second much lower, 
some ten feet back of the front one. ‘These are bound together, 
and secured by ties running from one to the other. On these 
tiers of logs each rafter rests, with its foot on the solid rock at the 
bottom of thedam. The base is covered with gravel about three 
fifths of the distance towards the top. The vibrations are most 
remarkable when the sheet of water is about four or five inches 
deep. A gentle breeze up the stream is said to be most favorable 
to the vibrations, but a-high wind, disturbing the falling sheet of 
water, in a measure: destroys the effect. An unbroken sheet the 
whole length of the dam is necessary to get the greatest effect, and 
an unbroken sheet to a considerable extent to get any effect. Any 
article, whether light or heavy, resting on the edge or top of the 
dam, thereby separating the sheet of water, impairs the effect, and 
hence arises the practice of nailing strips of board every twelve 
or twenty feet to destroy the vibrations. This is an infallible 
remedy. Mr. Osborn has resorted to it yearly for fifty years. It 
has been his uniform custom to cause strips of board from six to 
twelve inches in width to be nailed with their ends projecting 
beyond the dam sufficiently far to divide the sheet of water. The 
width of the boards must be taken into account. It is found 
from experience that the narrowest ones must be placed nearest 
together, while the wider ones will bear to be separated a greater 
distance. These pieces usually become torn off during the win- 
ter and spring freshets, but the vibrations are not felt at all while 
the water is high, or while the sheet that pours over the dam 
much exceeds four or five inches in depth. A sheet of water of 
much more than this depth falls with a smooth unbroken surface, 
and without vibratory motion. = 
