His results are purely observational. The velocities can be measured by measuring how redshifted nebulae spectra are, while distance estimation is a little bit more sophisticated. You want a source with known luminosity, only then you can measure how far it is. A supernova explosion is one such a tracer, and Cepheid stars are another (but you have to measure the period of the star first).
Also, since I'm replying to a very old question and feel guilty about it, can anybody recommend me a classical paper on jet formation?