252 Literary and Philosophical Society. 



expenditure of moving force in overcoming cohesion of 

 particles of fluid, he refers to the case of a jet of water 

 issuing from a hole in the containing vessel — this had been 

 considered by John Bernouilli in his ' Hydrodynamics. 

 Newton also considered it ; his solution in later editions 

 of the * Principia ' differing from that in the first. To 

 measure the repulsive action on the water in the opposite 

 direction to the jet Newton suggested that the vessel 

 should be suspended like a pendulum ; it will then recede 

 from the perpendicular in the opposite direction to the jet. 

 Ewart made some experiments of the kind, and obtained 

 results nearly agreeing with what it was concluded to be 

 by Bernouilli and Newton. The results also agree with 

 the explanations that have been given of moving force. 

 Upon the same principle an easy and simple explanation 

 may be given of the action of the hydraulic machine called 

 Barker's Mill. The theory of this machine has engaged 

 the attention of many mathematicians, and Euler has 

 furnished two treatises on it to the Memoirs of the Berlin 

 Academy — his demonstrations are complicated. Mr. 

 Waring in America has given quite a different theory. 

 Ewart's own explanation is different from any other ; allud- 

 ing to the maximum effect produced by machines, Ewart 

 observes that in the actual construction of machines it is 

 necessary to aim at a maximum quite different from that 

 which is usually proposed in books on the theory of 

 machines. By proceeding on the principle that when a 

 weight is raised from one point to another in the least 

 time the maximum effect is produced, many erroneous 

 conclusions have been drawn respecting the proper con- 

 struction of machines ; Ewart mentions an example in the 

 case of overshot wheels. Ewart next refers to a case 



