230 E. 8. Snell on the Waterfall at Holyoke. 
In a manner somewhat like this, a stream of air from the lips, 
driven across the embouchure of a flute, excites vibrations in the 
column of air, with such frequency that it can itself vibrate in 
unison with it. But, if the stream is blown more and more 
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breath produce six or eight harmonic notes on the flute, when 
all the fale are closed. 
At the time when I witnessed the comparatively slow oscil- 
lation of 82 per minute, I was surprised by the great strength of 
the current of air, as it rushed into the opening at the end of the 
am. I could not venture within the passage through the pier, 
lest I should be swept in behind the sheet; nor could I stand at 
the entrance of the arch, without bracing myself, by placing 
both hands on the corners. There was, however, no alternate 
outward blast, but only a lull, or cessation of all motion; which 
shows, that the excess of air that pours in at every pulse, is car- 
ied out again in some other way; and there is no conceivable 
way for it to escape, except to be driven down by the falling 
water, and poured up externally in a bed of foam. It had never 
occurred to me before, that the velocity of the air-current 
must be greater, the longer the interval between the pulses, 
since the rarefaction within the tube will be greater nearly in the 
ratio of the same interval. 
tothe air. But the rock and soil in the immediate vege! of 
j ile the 
water, and if so, that they cannot cause sensible undulations 
the earth, I am not prepared to assert; but I believe that any 
unbiased observer will tind it quite absurd to apply sueh an 
explanation to the strong puffing of the air which is usually s° 
noticeable at the Holyoke fall. 
