368 Vibrating Dams. 
tion, the foundations of both of these buildings resting on sand. 
It is not recollected that any vibrations have ever been noticed 
in the windows on that side of Mr. Osborn’s house’ which is 
turned directly from the dam. 
Il]. Dam at Springfield, Mass. 
The following is the substance of a letter from Mr. Amasa 
Holcomb, well known as the manufacturer of Herschelian tele- 
scopes. ‘The dam crosses Westfield River about two miles west 
of Springfield. It is four hundred and fifty feet long and seven- 
teen feet high, and stands on solid rock the whole length. It 
runs nearly north and south, and is perfectly straight and level 
on the top. ‘The water is taken from the dam in a canal about 
eighty rods to a paper mill; and where the dam joins the canal 
there is a strong breastwork of stone laid without mortar. Where 
the dam joins the bank at the south end, there is also a breast- 
work of stone, with an apron of plank for a few feet, on which 
the sheet of water falls and turns it to the north. All the rest 
of the sheet falls into water of six feet or more in depth, it hav- 
ing torn away the rock below the dam. 'The dam is of wood, 
framed. A row of posts about three feet apart are framed into 
the highest plate of the dam its whole length. The upper side 
of the dam has a slope apparently of 40° or 50°; but on the 
lower side, the water falls without obstruction the whole height 
of the dam. The dam is built in the best manner, and was very 
expensive. ‘T’he rafters are covered entirely with plank carefully 
jointed, and tight without gravel except at the bottom. ‘There 
may be some gravel washed on, but there is none to be seen. 
The water is now (Aug. 10, 1842) running over the dam to the 
depth of about eight inches. 'The most favorable time for vibra- 
tions is when the water isa little lower, but Iam told that it 
requires nearly the present amount to produce them. I will now 
describe the vibrations as intelligibly as I can. There is no wind 
and the surface of the pond is very smooth, perfectly so appa- 
rently, but the sheet of water is in waves, and the inequalities 
appear to commence immediately after the water leaves the dam. 
Standing on the stone breastwork at the north end of the dam, 
and looking south in the range of the dam, the top of it appears 
like a long stick of timber under water with the ends fast, but 
vibrating horizontally four or five inches in the middle. This 
