and 12 form a continuous fluid circuit wherein mercury may be supported and which freely moves to a position determined by the pressure differential between pressure outlets 19 and 26 pressure outlet 19 may be connected to a reference pressure and 26 may be connected to an unknown pressure to be measured the u tube structure of fig1 operates as a conventional manometer in that the column of mercury in each of legs 11 and 12 may freely move depending on the pressure differential applied to the manometer however the legs of the manometer 11 and 12 are radio frequency coaxial feedline structures these include an outer shell 20 and 24 containing an inner cylindrical conductor 17 and 23 the inner conductor 17 and 23 and outer shell 20 and 24 are spaced apart to provide a radio frequency coaxial feedline structure the inner conductors 17 and 23 pass through insulating pressure tight seals 22 although the example noted above uses mercury in a u tube manometer the principles of operation will also be the same using any other liquid metal as the working fluid also instead of coaxial radio frequency feed lines open wire radio frequency feed lines extending into glass tubes can be used in this case the liquid metal would provide an electrical short between the lines the u tube structure is not the only structure in which.