We present results obtained from a study of the structure of hadronic event
s recorded by the L3 detector at various centre-of-mass energies. The distr
ibutions of event shape variables and the energy dependence of their mean v
alues are measured from 30 GeV to 189 GeV and compared with various QCD mod
els. The energy dependence of the moments of event shape variables is used
to test a power law ansatz for the non-perturbative component, We obtain a
universal value of the non-perturbative parameter alpha(0) = 0.537 +/- 0.07
3. From a comparison with resummed O(alpha(s)(2)) QCD calculations, we dete
rmine the strong coupling constant at each of the selected energies. The me
asurements demonstrate the running of alpha(s) as expected in QCD with a Va
lue of alpha(s)(m(Z)) = 0.1215 +/- 0.0012 (exp) +/- 0.0061 (th). (C) 2000 E
lsevier Science B.V. All rights reserved.