The purpose of the work was originally to extend work of Dr. G. W. Stewart on Acoustic Wave Filters in Air to the case where the transmitting medium is a solid. Due to the fact that transmission in solids consists of two types of waves, it is not possible to apply the original theory and recourse must be had, at least in the first instance, to experiment. The problem thus became one of finding an empirical formula which would aid in working out a special approximate theory for these filters
