462 SEC. 12. APPLIED MECHANICS. 



from rivers or streams descending from higher ground in proximity to the 

 low \vet ground. The jet pump is not necessarily arranged in conjunction 

 with an intermittent reservoir, but may be used alone in many cases for 

 raising water by the power of other water descending to the available outfall 

 level from above. A general notion may be formed of the mode of action of 

 the jet pump by conceiving the action as being somewhat like that in a loco- 

 motive steam-engine chimney, with the substitution of an impelling jet of 

 water instead of the impelling jet of steam, together with the substitution of 

 water drawn from the low laud instead of smoke drawn from the fire. The 

 part corresponding to the chimney must have a narrow throat at the place 

 where the jet enters, and must thence widen very gradually towards its outlet 

 end. It is usually convenient to have it inverted, as compared with the 

 chimne} r , so that the jet shall shoot downwards ; and the discharging end of 

 the pipe corresponding to the chimney must be immersed in the outfall water, 

 so as to prevent any admission of air during the pumping action. The water 

 is drawn up from the low ground by a suction pipe, terminating in a chamber 

 surrounding the jet nozzle. Now, since the jet pump, Avhen wanted to be 

 applied for drainage, must be made large enough to do the work of flood times, 

 it would be much too large to work continuously in dry weather, and, therefore, 

 it is made to work intermittently, by the arrangement, in conjunction with it, 

 of an intermittently flowing reservoir. The reservoir is made to receive the 

 continuous but variable supply of water for power coming from the higher 

 ground, and to give it out intermittently to the jet pump. The intermittent 

 action is brought about in a very simple way by means of two syphons. The 

 whole arrangement here described was contrived many years ago by Professor 

 Thomson, and brought, with entire success, into practical use on the lands of 

 William Forster, Esq., of Ballynure, Clones. It is free for general use 

 wherever applicable, not being the subject of a patent. 



1996. Working Model of a Hydraulic Bam, arranged 

 with glass air vessels, so as to show the action of a column of air 

 and pulsations of delivery valve. K. W. Hedges $ Co. 



2213. Apparatus for showing the Motion of Fluids 

 through long Tubes. T. Hawksley. 



V. FIRE ENGINES AND PUMPS. 



2053. Pneumatic Pump, with taps. Invented by 'sGrave- 

 sande. Prof. Dr. P. L. Rijke, Leyden. 



The taps are at each stroke of the piston turned 90 by an appliance in 

 the form of a cross fixed to the handle. (See 'sGravesande's " Physices 

 Elementa Mathematica," ed. III. vol. II., p. 591.) - 



2O2O. " A new Water Engine for Quenching and Ex- 

 tinguishing Fires." H.M. Commissioners of Patents. 



This engine is made under patents No. 439, A.D. 1721, and No. 479, 

 A.I). 1725, granted to Richard Newsham, pearl button maker, of London, 

 and is one of the first engines in which two cylinders and an air vessel are 

 combined and worked together so as to ensure the discharge of a continuous 

 and uniform stream of water with great force. This invention of Newsham 

 still exists in all fire-engines of the present day, with improvements in 

 materials, workmanship, and the application of steam power. 



