The steam from the boiler, passing through the pipe _A_, enters the _receiving-tube C_. Here it is joined by the water which enters the pipe _B_. The water condenses the steam in the _combining-tube D_, and a water jet is formed which is driven across the _overflow_ space _F F_, and enters the _delivery-tube H_, thence past the _check-valve I_ into the boiler. During the passage of the water from _D_ to _H_, as it passes across the _overflow_ space _F_, if too much water has been supplied to the steam, some will escape at this point and flow out through the _overflow nozzle G_, while if too little water has been supplied, air will be drawn in at _G_, and carried into the boiler with the water. The names of the essential parts seem very applicable when we notice that steam is _received_ from the boiler at _C_, _combines_ with the water at _D_, and both are _delivered_ to boiler through _H_. QUESTION 133. _How is the operation of the injector explained?_ _Answer._ Steam escaping from under pressure has a much higher velocity than water would have under the same pressure and condition. The escaping steam from the _receiving-tube_ unites with the feed-water in the combining-tube, and gives to this water a velocity greater than it would have if escaping directly from the water-space in the boiler. The power of this water to enter the boiler comes from _its weight_ moving at the _velocity_ acquired from the steam, and it is thus enabled to overcome the boiler pressure. This can be illustrated with a wooden croquet ball, which will float on the surface of water and will require considerable force to make it sink. If, however, it is thrown violently into the water, it will sink to a considerable depth before its buoyancy will overcome its momentum, or _actual energy_. If, however, we were to take a very light, hollow wooden or india-rubber ball, no matter how violently we throw it into the water, it will not sink, because the total _actual energy_ of any body IS PROPORTIONAL TO ITS WEIGHT MULTIPLIED BY THE SQUARE OF ITS VELOCITY, and therefore if we throw the hollow ball at the same velocity as the solid one, the former will still have much less energy than the latter. Now, as already stated, steam under a given pressure escapes from an orifice with a very much greater velocity than water. But steam being very light, if its weight is multiplied by its velocity its total energy will be comparatively small. Now in the injector, a portion of the high velocity of steam is imparted to the heavy water, because this water is presented to the action of the steam, not in a mass, as in the boiler, but in small quantity and in such a position that it can easily escape, so that it gradually acquires as high a velocity as the escaping steam can impart, and at the same time the steam is condensed, and therefore there is a heavy substance with a high velocity, whose actual energy is sufficient to overcome the pressure in the boiler.