Bauhaus-Universität Weimar

On sound and atmospheric vibrations, with the mathematical elements of music
Airy, George Biddell
into different positions, and of the vanishing of the 
sound in some positions (Article 49). 
Among the special experiments on the vibrations of 
air in musical pipes, we know none so important as 
those by the late Mr Hopkins, published in the Trans¬ 
actions of the Cambridge Philosophical Society, Yol. v. 
The vibrations of air at the mouth of the pipe were pro¬ 
duced by the vibrations of a plate of glass, vibrating 
(apparently) in a known time: it was found that a 
small distance of the glass-plate from the pipe made 
the phænomena the same as if the pipe had been quite 
open to the external air (as the experimenter who uses 
a tuning-fork will also find), but with particular cautions 
in some instances the phænomena were made identical 
with those which belong to a closed pipe. The exami¬ 
nation, however, in which Mr Hopkins was most suc¬ 
cessful was the determination of nodal points; which 
was effected by gradually lowering into the tube a 
stretched membrane carrying a very small quantity of 
sand, and noting its place when the sand was not 
shaken by the air. It was thus found that the node 
next to the open mouth of the pipe was somewhat less 
distant from it than that given by theory (Article 79) ; 
or, which amounts to the same thing, that the place 
where the air has always the same density as the 
external air is not exactly at the pipe’s mouth but 
somewhat exterior to it (as is suggested in Article 79). 
The experiments, generally, were experiments on reso¬ 
nance ; and in one of these, Mr Hopkins appears to 


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