223 



MACHINERY IX COXNECTIOX WITH WATER. 



the upper one, and being furnished with a regular succes- 

 ^^s-249. sion of metallic discs, which 



nearly fit the bore in the tube, 

 a, the water is carried up in 

 large quantities. When the 

 motion is discontinued, the 

 water settles down again into 

 the well, and consequently 

 this pump is not liable to- 

 accident by freezing. By 

 sweeping rapidly through the 

 water, it preserves it in better 

 condition, and prevents stag- 

 nation. The friction being 

 very small, it will last a long 

 time without wearing out. 



llotary Pumps. A succes- 

 sion of cavities made in the 

 exterior of a short cylinder 

 receive the water from the 

 pump-tube below, and force 

 it away into the elevating 

 tube. When driven fast, it 

 pumps with great rapidity. 

 It possesses this advantage 

 over the common pump, that 

 the motion being continuous, 

 no force is lost by repeatedly 

 checking the momentum. In 

 the figure on the preceding 

 page, the pump is represented 

 as inserted in a barrel of oil, 

 which is to be emptied into 

 the reservoir above, and is 

 Suctim and Fordng-pump. worked by hand. Larger 



rotary pumps are driven by horse and steam power. 



