A resonance tube is a closed pipe with adjustable water level. For a tuning fork of frequency $f$: first resonance at $L_1 \approx \lambda/4$, second at $L_2 \approx 3\lambda/4$, third at $L_3 \approx 5\lambda/4$. $L_2 - L_1 = \lambda/2$ and $L_3 - L_2 = \lambda/2$. Speed of sound: $v = f\lambda = 2f(L_2 - L_1)$. The ratio $L_1:L_2:L_3 = 1:3:5$ (approximately, ignoring end correction). With end correction: the ratios are slightly different.