416 Mr. Ewart on the Reaction oj 'effluent Water, 



colouring 'painted, on either retina, by which the separation of 

 their forms can be distinguished ? 



Press the axis of either eye sufficiently to the right or left, 

 a larger quantity of colouring will immediately be painted upon 

 one retina than upon the other, which will separate their in- 

 terior and horizontal edges, and two images will thence imme- 

 diately and necessarily arise upon the perception of the mind. 



I feel convinced that the more these ideas are contemplated, 

 and the more clearly they are apprehended, the better will they 

 serve to elicit the reason of several other phaenomena concerning 

 vision, which it has hitherto been considered difficult to ex- 

 plain; and«what is of still greater importance, they may throw 

 some light upon those which belong to every analogous ope- 

 ration of the human senses and intellect. 



LXIV. On the Reaction of effluent Water, and on the Maxi- 

 mum Effect of Machines. By Mr. P. Ewart*. With Notes 

 relating to the Theory of Barker's Mill. By J. Ivory, Esq., 

 M.A.F.R.S.f 



r T , HE following important proposition relating to this sub- 

 -*• ject, is laid down by Daniel Bernoulli in his " Hydrody- 

 namics," page 278. If a jet of water I (fig. 1.) issue from the 

 side of a vessel A, with the velocity which a body w r ould ac- 

 quire in falling freely from the surface B to C, he says the re- 

 pulsion of the water in the opposite direction to the jet will be 

 equal to the weight of a column of water, of which the base is 

 equal to the section of the contracted vein, and the height 

 equal to 2 BC. 



This question respecting the amount of what has been termed 

 the " reaction of the effluent water," derives additional interest 

 from the circumstance of its having particularly engaged the 

 attention of Sir Isaac Newton, and from his having given a 



* From a paper " On the measure of moving force," in the Memoirs of 

 the Lit. and Phil. Society of Manchester, second series, vol. ii. 1813. 



We insert this extract because it treats, correctly we believe, of subjects 

 which have engaged the attention of many eminent mathematicians (in 

 former times as well as recently), whose reasonings and conclusions on the 

 points in question are at variance with each other. These discrepancies 

 are to be regretted, inasmuch as some of the essential points in the appli- 

 cation of the principles of mechanics to practical purposes are involved in 

 them. — Edit. 



t Communicated by the Author. 



We are glad to lay before those of our readers who have attended to the 

 various intricate theories that have been offered of the action of Barker's 

 Mill, Mr. Ivory's Notes on that subject — Edit. 



solution 



