Supersonic dispersion in gases and liquids still attracts the majority of workers in this field. We shall first deal with the published work in 1937 which forms an extension of the matters which were treated in a special Report in Volume 4.Taking first the work on gases, we find that Hodge and Hubbard("*) have extended the earlier measurements on the change of supersonic velocity with pressure up to IOO atm. using a Pierce interferometer and five frequencies from 88 to 500 kc./sec. The chamber was constructed out of a block of steel with a cap which could be removed to replace the quartz oscillator. The metal to metal joint which permitted the apparatus to be sealed was made by cutting a circular V-shaped ring into a soft copper gasket with sufficient force to cause the copper to flow. The force to do this was applied by screwing down two bolts with a wrench, making a gas tight seal even at IOO atm. The pressure was measured on a Bourdon gauge. For the results : a steady rise was observed in hydrogen, helium, oxygen and nitrogen, but a fall with increasing pressure was apparent in carbon dioxide, No evidence of the usual S-shaped curve, observed in the case of carbon dioxide by earlier workers, appears in the results, but this is possibly because pressures below atmospheric were not applied. In conjunction with known values of compressibility, the ratio of specific heats for these gases at various pressures is then deduced. Eucken continues his work, this time in collaboration with nu man^^(^), on gases at high temperatures.Both absorption and velocity in the dispersive gases, carbon dioxide and nitrous oxide, are measured up to 400' c., with attendant variations of pressure from normal up to 4 atm. and a single frequency of 200 kc./sec. The reflector is kept at a fixed