THE STEAM-ENGINE. 16 9 



the arrogance, I am sorry to say, common to many of us, 

 I said, " nonsense," and we all said " nonsense," and there 

 was a chorus of " nonsense," and nonsense it was, for we had 

 to go and see it at work, and there was no doubt about the 

 result. Then came the question why it worked. Why did 

 we see the steam re-enter the boiler from which it had 

 started 1 There have been a great many papers written upon 

 this subject in a mathematical form, but I have said on 

 more than one occasion, that I arrogate to myself, rightly or 

 wrongly, the credit of being the first to give a popular ex- 

 planation of the action of the injector. I believe the whole 

 theory is to be explained by one word, and that is " con- 

 centration." Let me illustrate what I mean. Supposing 

 there were a cistern containing water with a nozzle upon the 

 side of it near the bottom, from which the water could issue 

 horizontally in a jet. Assume the jet were opposite to an 

 orifice in an empty cistern parallel with the first. We 

 know that the jet of water would enter that orifice, that 

 the water would accumulate in the cistern which the jet 

 entered, and that the jet would continue to enter until 

 the accumulated water in the second cistern caused the jet 

 to have such an opposition that it could not enter. Now 

 Mr. Froude has shown us in his experiments that when you 

 have once got the water into motion, if you will allow a 

 sufficient difference of head between the two cisterns to 

 compensate for the resistance caused by the friction in the 

 tubes through which the water passes, the water will, if you 

 have a proper nozzle, continue to enter into the second cistern 

 when it is full up to the height of the first one, minus the 

 difference expressing the friction. We see, therefore, that we 

 may get the water entering the second vessel very nearly to 

 the height from which it issued from the first. But supposing 

 that the water in its passage across the imaginary space from 

 the vessel from which it flowed, to the one into which it is to 

 enter, could by some process of magic be converted into 

 mercury, the same weight of mercury as was equal to the 

 weight of water : we know that if we could do that we 

 should diminish the area of the stream to yj- or thereabouts, 

 so that the stream which came out of an orifice of a square 

 inch, when converted into mercury would enter the other 

 tank through an orifice of ^ of a square inch ; but the 

 stream being of the same weight and flowing with the same 



