REPORT ON CAPILLARY ATTRACTION. 259 



traction as the solid. Hence the truth of the proposition is 

 manifest. We shall have occasion in a subsequent part of the 

 Report to allude to this demonstration. 



In 1751, Segner*, aware that Clairaut had written some arti- 

 cles {" articulos quasi epi^odicos") on capillary attraction, but 

 not having seen his work, attempted to determine theoretically 

 the form of the surface of a drop of water resting on a horizontal 

 plane, on the hypothesis of the attraction of the parts of a fluid 

 for each other. This is a problem of the same nature as that of 

 determining the form of the upper surface of the column of fluid 

 sustained in a capillary tube, neither of which had yet engaged 

 the attention of mathematicians. Segner begins with admitting 

 the tenacity of fluids, and ascribes it to the action of an attrac- 

 tive force resident in their constituent molecules, the law of 

 which he does not pretend to assign, but assumes only that the 

 sphere of the activity of each particle is of insensible magnitudef. 

 Setting out with these correct principles, he is led to refer the 

 shape which the drop assumes to the action of its superficial 

 particles, which form, as it were, a sheet encompassing it, and by 

 their tenacity counteract the tendency of the drop to spread in 

 obedience to the force of gravity. The sequel of this essay is 

 not equally successfvil. In estimating the superficial tension 

 considered as depending on the curvature at each point of the 

 Surface of the drop, the author commits an error in taking ac- 

 count only of the curvature of the sections made by vertical 

 planes through its axis, and neglecting the effect of the curva- 

 ture in planes perpendicular to these. He intimates in a note 

 at the end of the essay that he became aware of some defect in 

 his theory. 



A considerable time after the theory of Segner was published, 

 Monge asserted, at the end of a memoir | on certain eftects of the 

 apparent attraction and repulsion of small bodies floating on 

 fluids, that " by supposing the adherence of the particles of a 

 fluid to have a sensible effect only at the svirface itself, and in 

 the direction of the surface, it would be easy to determine the 

 curvature of the surfaces of fluids in the neighbourhood of the 

 solid boundaries which contain them ; that these surfaces would 

 be linteari<E, of which the tension, constant in all directions, 



* Comment. Soc. Reg. Gotting. torn. i. Ann. 1751, p. 301. 



t " Generatim autem spatium illud sphsericum, intra quod particulse activitas 

 consistit, adeo exiguum est, ut nuUo adhuc sensu percipi potuerit." (p. 303.) 

 Segner appears to have been the first to apply to capillary phfenomena mathe- 

 matical calculation founded on this hypothesis. 



X Memoires de VAcad. des Sciences, An 1787, p. 506. 

 S 2 



