The OSO-8 satellite enabled us to study various characteristics of the profiles of Si 1I, Si Iv, C IV, and O Vl lines above active areas of the Sun, as well as above quiet areas, and to derive some physical properties of the transition region between chromosphere and corona (CCT): (i) The study of the lines shows a general tendency for the microvelocity fields on the average to be nearly constant for the heights corresponding to T > l0 s K; however they seem to slightly increase with height in quiet areas, and decrease in active areas. (ii) A multicomponent model of the CCT is however quite necessary, and its geometry is far from being a set of plane-parallel columns. It is similar to an association of moving knots within the non-moving principal component of the matter. (iii) The proportion of mass, in the knots relative to that in the non-moving component, is several times larger in active regions than in quiet regions. (iv) In the knots, the non-thermal mierovelocity fields are smaller in active regions and seem to decrease for Tincreasing above 103 K, contrary to what happens in the steady principal component. Of course, we consider that microturbulence and Doppler shift are two aspects of the same distribution of velocity.