Zl^ 



NA TURE 



[March 23, 1922 



perfectly definite statement that " the attractive Power 

 of small Particles of Matter acts only on such Corpuscles 

 as are in contact with them, or removed but infinitely 

 little Distances from them/' thus anticipating Segner 

 by nearly half a century.^ 



Obviously, it follows that (in anticipation of Clairaut) 

 the water in the interior of capillary tubes is held up 

 by the attraction of the particles of the walls of the 

 tube, to those particles of water at the surface which 

 are " urged strongly towards the Glass." Lastly, 

 Leslie was not the first to show that the attraction is 

 everywhere normal to the surfaces of the solid, as 

 Maxwell states, for Hauksbee says : " The Parts of 

 the Liquid adjoining to the concave Surface of the 

 Tube are strongly attracted by it, and that in a 

 Direction perpendicular to the sides of the Cylindrick 

 Glass." 



A comparison of contemporary references with the 

 actual writings of Newton leads to the conclusion that 

 much which is attributed to him was made public 

 verbally during the discussions at the Royal Society. 

 An interesting instance is furnished by the note to Dr. 

 Jurin's paper.^ At any rate, the hints scattered 

 through the Queries to his " Opticks " as to the exist- 

 ence of forces acting between the particles of matter 

 " which reach to so small distances as hitherto to 

 escape observation," and which sprang in the first 

 instance from his study of the diffraction of light, 

 became a compact body of doctrine accepted in England 

 before 1720. Hauksbee, as we have seen, wrote in 

 1709, nine years before the thirty-first Query was 

 published, of intermolecular forces of insensible range, 

 which fall off according to some higher power than the 

 square of the distance, and Jurin in 17 19 speaks of the 

 " universally acknowledged " attractive force between 

 the particles of a fluid (water), and refers to the spher- 

 icity of drops of rain, and the fusion of drops of water 

 when in contact, as examples of the operation of the 

 force ; in both cases reference is made to Newton. 



This doctrine, which, I believe, was shaped by .the 

 discussions at the Royal Society, may be embodied in 

 a series of propositions as follows : — 



(i) That, in addition to the force of attraction which 

 acts between larger bodies and varies in intensity 

 according to the inverse square of the distance, there 

 is another attractive force which acts between the 

 ultimate particles of matter, has a range of insensible 

 magnitude, and varies inversely according to some 

 power of the distance higher than the square. 



(2) At distances less than a certain minute value 

 this attractive force gives place to a repulsion. 



(3) The attractive force " performs the Chymical 

 Operation " ; it is the source of cohesion, and co- 

 hesion brings about the movement of fluids in small 

 spaces. 



(4) Heat is a quaUty of matter, not a substance. 

 It is the agitation of the particles of matter, and 

 if " the Heat is big enough to Keep them in (adequate) 

 Agitation, the Body is fluid." 



(5) The ultimate particles of matter are of definite 

 shapes — not always spheres — and are impenetrable. 



Dr. Jurin, secretary of the Royal Society during 

 a portion of Newton's term as president, was led to 



^ Maxwell therefore is wrong in saying that " these early speculators . . . 

 do not distinctly assert that this attraction is sensible "only at insensible 

 distance." 



' Phil. Trans., 355, p. 739, 1718. 



NO. 2734, VOL. 109] 



the subject of capillarity by " an ingenious Friend " 

 who proposed a plausible method for " making a per- 

 petual Motion " founded upon Hauksbee's experiments. 

 The method is of little interest, but Jurin was led 

 directly by it to the discovery that the height to which 

 fluid is raised is determined by the " periphery of the 

 tube to which the upper surface of the water is con- 

 tiguous," and he argues that, as this is the " only part 

 of the tube from which the water must recede upon 

 its subsiding," it is consequently " the pnly one which 

 by the force of its cohesion or attraction opposes the 

 descent of the water." Hence the rise must be in- 

 versely proportional to the diameter of the tube. 

 Newton and Machin pointed out that Jurin's " ' peri- 

 phery ' ... is really a small surface, whose base is 

 that periphery (of the tube), and whose height is the 

 distance to which the attractive power of the glass is 

 extended." ^ 



In the interval between Jurin's papers a book 

 appeared " by a very learn'd and ingenious member 

 of this [the Royal] Society," whose name I have 

 not succeeded in tracing. It deserves mention because 

 in it the effect of the attractive power of the water for 

 itself is exactly considered. Jurin demonstrated the 

 attraction in a striking manner when he showed that 

 if the tube at the lower part of a funnel is drawn out 

 to capillary dimensions and the funnel inverted with 

 the open mouth under water, then if it be filled by 

 drawing water up into the capillary it will remain full. 

 The experiment succeeded in a vacuum. H-e infers that 

 the lower mass of water in the funnel must be suspended 

 by its cohesion to the column within the capillary. At 

 the end of the memoir is a series of propositions, of 

 which Nos. 4 and 6 assert that the particles of water 

 are more strongly attracted by glass than by each other, 

 but the particles of quicksilver are attracted more 

 strongly by each other than by the glass — hence the 

 rise of water and the depression of quicksilver in a tube. 



Though the theories of Hauksbee and Jurin were 

 generally adopted — as, for instance, in the memoirs 

 of Bilfinger * and Weitbrecht ^ — there was a body 

 of opinion which contested the existence of attractive 

 forces of cohesion.^ 



The cause of this widespread interest and discussion 

 of capillary phenomena in the eighteenth century 

 cannot be better stated than in the words of the 

 astronomer, de la Lande '^ : " Many phenomena are 

 regarded as allied to those of capillary tubes, . . . e.g. 

 the suction of sugar and of sponges, the origin of springs 

 in elevated sites ; the secretions in the human body 

 seem to be due to the same cause. . . ." These pheno- 

 mena illustrate the general attraction of matter, con- 

 tested too long. " Capillary tubes put into our hands 

 an obvious example of the generality of this law, which 

 is the keystone of physical science." But M. de la 

 Lande's attempts to explain the phenomena were not 

 very illuminating ! 



In the eighteenth century the force of cohesion was 

 so closely identified with chemical action that Guyton 



' Phil. Trans., 1718, p. 747. 



♦ Memoires de I'Acad. de St-Pdlenoourg, vols. 2 and 3, 1727-28. 

 ' Ibid., vols. 8 and g, 1736-37. 



• E.g. Paulian, " Traits de paix entre Newton et Descartes," vol. 3, 

 p. 199 ; Gerdil, " qui a fait un Livre tout entier centre I'attraction des 

 Tubes Capillaires " ; Abat and others. Mairan, who explained cohesion as 

 being due to electrical action, etc. 



' Journal des Sfavans (Amsterdam), vol. 35, November 1768, p. 75. 

 De la Lande, in his system of astronomy, incorrectly refers his own paper to 

 the October number. 



