What is the speed of sound in hydrogen if the fundamental frequency of a $\frac{2}{3} \mathrm{~m}$ long, open at both ends, and hydrogen-filled organ pipe is $h$?
The frequency $h^{\prime \prime}$ is 990. For open pipes, $n=\frac{c}{2 l}$, where $n$ is the fundamental frequency, $c$ is the speed of sound in the gas filling the pipe, and $l$ is the length of the pipe. From this,

$$
c=2 n l=1320 \frac{\mathrm{m}}{\mathrm{sec}}
$$

(Gauss Olivér, Csurgó.)

The problem was also solved by: Erdős A., Fekete J., Goldziher K., Kármán T., Szabó I.