325
Chap. 8.]
The front part of the cistern in which the pumps are fixed, is separatedby a perforated board from the hinder part, into which the water waspoured from buckets. The cylinders were four inches in diameter, andthe pistons had a stroke of ten inches. Each pump was worked by a sepa-rate lever, A A; an injudicious plan, since a very few hands could beemployed on each; and as the engine had no air vessel it was necessary,in Order to keep up the jet, that the piston should be raised and depressedalternately—a condition not easily performed by individuals unused to theOperation, and acting under the excitement of a spreading conflagration.The contrivance for changing the direction of the jet was very defective,and considering the date of this engine it is surprising that such a one wasthen in use. A short leathern pipe would have been much better. Itwill be perceived that the jet pipe is connected to the perpendicular orfixed one by a single elbow, instead of a double one, like the ordinarygoose-neck. The joints were also made differently. The short elbowpiece had a collar or ring round each end, and the jet and perpendicularpipes, where they were United to the elbow, the same. The faces ofthese collars were made smooth, so as to fit close to and at the same timeturn on each other : loose flanches on the pipes were bolted to others onthe elbow, and thus drew the^ collars together so as to prevent waterfrom leaking through. Now it will be seen that although the joint whichunites the elbow to the perpendicular pipe would allow the jet pipe to beturned in a lateral or horizontal direction, there appears no provision toraise or to lower it, and no apparent use at all for the other joint. Wewere at first at a loss to divme how the stream could be directed up anddown as occasions might require, for Belidor has not explained it; but onexamining more closely the figure in his work, we found that the jet pipeitself was not straight, but bent near its junction with the elbow : this dis-solved the mystery, for it was then obvious that by twisting this piperound in its joint, its smaller orifice could be inclined up or down at plea-sure. This very imperfect device is also shown in the next figure, thejet pipe being curved through its whole length, instead of a single bend asin the last one.
W&mm
The pumps of this engine are substantially the same as those of the last,but the piston rods are moved by a short vibrating beam placed directly