the intervals between the rings of moving vanes. Their concave sides also face towards the left, but, as seen in Fig. 38, their line of curve lies the reverse way to that of M M. Steam enters the casing at A, and at once rushes through the vanes towards the outlet at B. It meets the first row of fixed vanes, and has its path so deflected that it strikes the ring of moving (or drum) vanes at the most effective angle, and pushes them round. It then has its direction changed by the ring of F F, so that it may treat the next row of M M in a similar fashion.
THE EXPANSIVE ACTION OF STEAM IN A TURBINE.
On reaching the end of D1 it enters the second, or intermediate, set of vanes. The drum here is of a greater diameter, and the blades are longer and set somewhat farther apart, to give a freer passage to the now partly expanded steam, which has lost pressure but gained velocity. The process of movement is repeated through this stage; and again in D3, the low-pressure drum. The steam then escapes to the condenser through B, having by this time expanded very many times; and it is found advisable, for reasons explained in connection with compound steam-engines, to have a separate turbine in an independent casing for the extreme stages of expansion.