4IS ./. LrC(,titr- Aj>i><ir<i<i Attrtirtion* iiml /,'> jnil.sJo/ts 



pressure of the atmosphere as a fundamental element into their 

 explanations of these motions. Indeed, Laplace himself seems 

 to have been impressed witli the apparent conflict between 

 theory and experiment : for, alter giving the result in relation 

 to the case of two solids moistened b\ the liquid (in which the 

 hydrostatic pressure between them has a negative value), he 

 v adds: " Dans le vide, les deux plans tendraient 

 encore a sc rapprooher ; 1'adhorcnoe du plan an 11 aide, produis- 

 ant. alors !<• meme effect que hi pressure de I'atmosphere."* 



Doubtless, the view, which ascribes these apparent attractions 

 and repulsions to the modifications of hydrostatic pressure due 

 to the action of capillary forces, is a philosophical one and 

 capable of being put into a mathematical form; yet, when the 

 physical < ius< ot tin [isturbni oi hydrostatic equilibrium is 

 kept in the back ground, the student is greatly embarrassed 

 and perplexed in obtaining clear conceptions oi' negative and 

 positive pressures, complicated as they are with considerations 

 relating to the pressure of the atmosphere : especially when he 

 is assured, that the last-indicated pressure must be inoperative, 

 from the experimental fact, that the phenomena take place in 

 vacuo. Moreover, from this point of view, he is liable to lose 

 siuht of the real physical cause of all capillarv phenomena, 

 viz :— the reaction of the tense superficial film of the liquid, — 

 the true and efficient cause of the disturbance of hydrostatic 

 pressure. It seems to me, that by referring the motions of 

 such bodies directly to the action oi' this tensile superficial lihn. 

 a fundamental principle in the physical theory of capillarity is 

 secured in the mind of the student; while the resulting dis- 

 turbances of hydrostatic equilibrium are not primary facts, 

 but secondary consequences of the more fundamental cause. 



The general explanation, which I am about to offer of the 

 " Apparent Attractions and Repulsions of small Floating 

 Bodies," is so simple and obvious a deduction from the funda- 

 mental Laws of Capillarv Action, as expounded by Laplace 

 and Poisson, that it is difficult to brin.tr myself to believe, that 



it has hitherto escaped the attet 



ition of 



physicists. Neverthe- 



less, I have not, thus far, been 



able to 



find it in any of the 



treatises on physics. 







In order to" render my expl 



anat ion 



more clear, it will be 



necessary to present the coumu 





e their delects. 



tionsof th.se phenomena, and t. 





Two methods of experiment. 



illustr: 



ition may be adopted. 



viz: 1st. By floating in water V 





bodies whose surfaces 



have been so prepared as to be 1 

 liquid : and 2d. By plunging v< 





d or non- moistened by 





into water or into mer- 



cury, two parallel plates ol cleat: 





ispended by threads. 



