208 Mr. C. Brooke on Negative Fluid 



been ascribed to " lateral action ; " which in reality does no more 

 towards their elucidation, than did of old the " principle of suc- 

 tion " for the explanation of the lifting-pump. 



In reference to Bernouilli , s experiment, I proceed to observe:— 



" This physical fact may probably be best explained thus : — Each 

 moving particle has acquired a certain amount of energy, by which 

 it exerts a pressure in the direction of the axis of the tube through 

 which it is passing. If flowing towards the smaller end of a conical 

 tube, Ain the figure, this pressure, a b, may 

 be resolved into a c perpendicular, and c b 

 parallel to the side of the tube ; of these 

 d c is wholly effective against the side of 

 the tube, and if an aperture or lateral 

 branch exists the fluid will escape thence. 

 If, on the contrary, the fl aid flow towards 

 the larger end, as in B, then c b, the por- 

 tion of the pressure a b resolved perpendi- 

 cularly to the side of the tube, acts en- 

 tirely from its surface ; and if a lateral 

 branch, entering the tube at a right angle, 



be immersed in a small vessel of fluid, atmospheric pressure on the 

 fluid in the vessel being transmitted through the branch- tube, and 

 unopposed at its point of junction, will cause the fluid to enter the 

 conical tube at that point. And it is evident that the greater the 

 value of c b, that is, the greater the velocity in the conical tube, the 

 greater will be the lateral influx ; this result is confirmed by experi- 

 ment ; for as the velocity of the fluid in B increases, that in the 

 lateral branch may be raised through a higher vertical column." 



In this case it is clear that the pressure of the fluid against the 

 interior of the diverging tube is, according to ordinary geome- 

 trical language, negative. Precisely the same reasoning will 

 apply to Desormes's experiment, because the space between the 

 parallel plane surfaces may be conceived to be made up of a 

 number of radial wedge-shaped diverging tubes. 



In the experiments, however, which have induced these remarks, 

 the negative or diminished pressure on certain orifices is due, not 

 to the resolution of a statical pressure, but to very different causes. 

 In the experiments of Mr. Hod well (and in analogous experi- 

 ments by Professor Magnus, published in your Number for Ja- 

 nuary 1851), the existing negative pressure appears to me to be 

 fully explained by cohesion existing between similar, or adhesion 

 between dissimilar molecules ; and that these forces are sufficient 

 may, I think, be inferred from the fact that a column of water 

 about two feet high, and of sulphuric acid nearly four feet high, 

 may be sustained in a very nearly exhausted and sealed vertical 

 glass tube merely by the cohesion of the fluids themselves, and 

 their adhesion to the surface of the glass. 



