From differential equations describing the behavior of a gas in a cylindrical tube are derived the characteristic impedance and propagation constant, analogous to similar quantities in the electrical transmission line. Curves are presented from which these quantities and others can be easily derived for dry air, knowing the driving frequency, mean temperature, mean pressure, and tube radius. Zero temperature variation and gas velocity at the tube wall are assumed. The equations include temperature, particle velocity, pressure, viscosity, thermal diffusivity, density, compressibility, and frequency. Experimental data on a tube 1/16 in. in internal diameter at driving frequencies from 2 to 29 cps are compared with the theoretical curves of characteristic impedance and propagation constant derived from theory. The agreement between theory and experiment is shown to be excellent. The design curves and procedure should prove helpful in the design and performance prediction of aircraft instrumentation systems. Curves are also presented from which the impedances of acoustic cavities can be computed. Experimental tests confirm these to an accuracy sufficient to justify their use in design. An outline of the experimental procedure and equipment is presented. (The work was done in the Physical Research Laboratory of Boeing Airplane Company.)