...Q j..„,& 



1876.] 311 [Briggs. 



one-fourth), because till the motion of the particles is purely parallel to 

 the axis, there must be some accelleratioa to be eflfected in the direction of 

 the axis, and this demands the employment of some vertical pressure. * * 



"In the vena contracta experiment with the thin plates and open air 

 between the plates, the fluid was welcome, if it pleased, to start tangential ly 

 to the plane of the aperture as here indicated, and 

 as it appears to do if closely studied. So also with 

 the introverted cylinder; although it was not possi- 

 ble to see what happened I have no doubt that- 

 the motion of the particles next the edge was ver- 

 tical upwards, the curvature being only such as 

 the pressure in the contiguous stream would satis- 

 fy. If the experiment was not adroitly initiated, 

 the water seized the inner surfaces of the cyl- 

 inder and run out in an eddied condition, fill- 

 ing the discharge pipe. When, however, it 

 was properly started, the contracted column be- 

 low issued with beautiful smoothness and sym- 

 metry." 



The second paper on the subject is an extract ^^ 



from a letter of Sir Isaac Newton to Professor Cotes, March 24th, 1710-11; 

 from the " Gorres'pondence of Sir Isaac Neicton and Professor Cotes, includ- 

 ing Letters from other eminent men," published in 1850, by Mr. J. Eddie - 

 stone. Fellow of Trinity College, Cambridge, from the originals in the Li- 

 brary of Trinity College. This letter possesses much value as showing New- 

 ton's experiment and discussions of the form of the vena contracta, and will 

 be found interesting to examine in the proceedings of the Glasgow Society 

 by those who have not ready access to the primary publica1>ion. Newton 

 found the vena contracta from an aperture in the side of a vessel of thin 

 sheet tin plate, five eighths of an inch in diameter, to have, at the distance 

 of one-half an inch from the hole, a diameter of 21-40ths of an inch. 

 Which was a reduction of diameter of 21-25ths, and of areas of cross sec- 

 tion of 0.7058. 



A foot note to this letter of Newton by Mr. Eddlestone says, that ' Sectio 

 vena contracta' was a term used by Jurin, Philosoph. Trans., Sept. — Octo. 

 1722, p. 185; and that Dan. Bernouilli uses the same term, Hydrodynam., 

 p. 65. Jurin also uses ' vena contracta ' ; in all these cases the words de- 

 note the reduced section only, while subsequent usage generally applies 

 them to the stream itself as a body, between the orifice and the point of 

 reduced section. 



The third paper is a discussion of the vena contracta by Professor James 

 Thomson, LL.D., C. E., University of Glasgow, and is a mathematical 

 discussion with six illustrations, intended to demonstrate under certain 

 conditions, as for instance the supposed absence of fluid friction or viscosity, 

 and a supposed great magnitude of vessel and depth of water compared 

 with the dimensions of the orifice, that the jet of water issuing from an 



