The differential equation for the flow of sound energy in a room of volume V yields two useful relations for determining a, the total sound-absorption in a room— one for the steady state, namely, a = 4E/vI0, and one for the decay, namely, I = I0e(av/4V)t. (E=rate of emission of sound-source, v = velocity of sound, I = average value of the instantaneous energy density, and I = the average value of the steady state energy density.) The advantages and limitations of different methods which utilize these fundamental relations are discussed. A method utilizing the steady state relation has been developed which exhibits considerable promise as a practical and precise means for measuring the sound-absorption in a room. The difficulties usually encountered from variations of intensity owing to the stationary wave-pattern in the room are overcome by a variable frequency source which varies periodically between limits of 408 and 629 d.v. This shifts the interference pattern sufficiently to give approximately an average intensity of sound at any point in the room not too near the source. Measurements of a obtained by this method agree satisfactorily with values obtained by the reverberation method for a frequency of 512 d.v. Results obtained by Meyer and Just and also by the writer indicate that it is possible to obtain photographic records of the decay of sound in a room from which it is possible to calculate the total absorption in the room. Measurements of absorption obtained by this method agree, with a probable error of about ten per cent, with those obtained by the reverberation method