L. Loomis on vibrating Water-falls, 355 
of 22 degrees. Professor Snell has observed the vibrations at 
six different times, and with the following average results (this 
Journal, vol. xxviii, p. 229). 
When the water ( 1 foot in height, the number ( 2574 per minute. 
on the edge 2 feet = of vibra- 4 137% 3 
of the dam is ( 5 feet - tions i 82 6 
I have spent considerable time at Holyoke, for the purpose of 
determining the number of vibrations corresponding to different 
depths of water. I visited the place in August, 1859, but there 
were Only 6 inches of water on the crest of the dam, and the 
vibrations were not noticeable. I obtained the engineer’s plan 
of the dam, from which 2 
5 n 
July, 1860, I spent seve- 
ral days in observations, 
: : : Ne 
uring which time t 
from two feet to one foot; 
and again in April, 1861, 
when I saw the water on 
the crest of the dam in- 
crease from 43 inches to Ss 
100 inches. The vibra- EZ 
tions ceased altogether “A 
after the water had risen 
indicated by the letter G. At each of srft 
my observations, I recorded the depth STONE 
of water by this gauge; and when the ABUTMENT 
as 
too great to allow this mode of measurement, I measured the 
difference of level between the surface of the water at the gauge, 
Am. Jour. Sct.—Srconp Serres, VoL. XXXVI, No. 108—Nov., 1863. 
46 
