Hi The primary reason for mercury was the slow propagation time, not impedance. The slower, the more bits per length. Mechanical transformers are not all that hard to create. Early programmable calculators use a different mode of transmission. They use rotation of a wire. The twisting goes slower along the wire than a compression wave because it is the rotational inertia compared to the spring of the wire. Compressional waves tend to travel faster. In something like mercury, being a fluid, can only transmit compressional waves ( except other surface waves like ocean waves ). A wire can use either compressional or rotational. The rotational is slower and can hold more date for distance. The important thing for any of these is absorbing any reflection. This means that impedance matching and possible dampening will make all the difference. Surface can have vertical as well as shear waves but these are harder to control. The rotational wave is similar to a shear wave. Dwight _________________________________________________________________ Get the power of Windows + Web with the new Windows Live. http://www.windowslive.com?ocid=TXT_TAGHM_Wave2_powerofwindows_122007