Makcii 23, 1922] 



NA rURE 



375 



Historical Notes upon Surface Energy and Forces of Short Range. 



By W. B. Hardy, Sec. R.S. 



'HE following notes were completed about fifteen 

 years ago for a purpose not now likely to be 



ilfiUed. They seem worthy of publication because 



le early history of the subject, which is to be found in 

 illlerk Maxwell's essay on " Capillary Action," ^ and is 



ised upon a report made by Challis to the British 



ssociation in 1834, seems to be wrong in material 



)ints. Challis does less than justice to the eighteenth- 

 ''century philosophers. 



According to Poggendorflf, Leonardo da Vinci must 

 1)6 considered as the discoverer of capillary phenomena, 

 but a fact so patent to all can scarcely have been dis- 

 covered by a single man. The ascension of water and 

 other liquids in capillary tubes was " noticed by the 

 Academy del Cimento at Florence early in the seven- 

 'eenth century, but seems not to have been much 

 (garded in the sequel." ^ Communications to that 

 uademy were anonymous. Probably Leslie's authority 

 was " une anecdote curieuse qui a ete publiee par M. 

 Nelli (' Saggio di storia letteraria,' etc., p. 92) sgavoir 

 lue le veritable auteur de cette experience fut Nicolas 

 Vggiunti, mort le 6 decembre, 1635 • • • ^'un des 

 Fondateurs de I'Academie del Cimento." ^ 



The beautiful volume issued by the Academy in 

 1667 is devoted mainly to experiments in a vacuum. 

 Amongst these is a demonstration of the rise of fluid 

 in a capillary tube in vacuo. 



The phenomenon was still novel when Boyle demon- 

 t rated capillary rise "to the no small wonder of 

 \ arious mathematicians." * Boyle tried, but failed, to 

 observe whether the rise took place in a vacuum, and 

 he also inquired why the capillary surface should be 

 concave with water and convex with mercury. 



If Leslie is to be trusted, the revival of the subject 

 was part of that great revival of physical experiment 

 which followed the promulgation of the Newtonian 

 system at the close of the seventeenth century. At any 

 rate, though Hauksbee was the first whose published 

 work needs consideration, he was not the first to make 

 experiments, for he writes of many attempts to " solve 

 this Appearance. . . . Some have argued from the 

 impeded or diminished Action of the Air,^ others from 

 the Innixion or Resting of the Parts of the Fluid on 

 the Pores and Asperities of the Glass ; others again 

 from the Congruity and Incongruity of the Parts of 

 Matter one to another." ® 



Argument was direct and frequently personal in the 

 pamphleteering times of the eighteenth century, and 

 Hauksbee goes on to say that the " First two ways of 

 solving the Difficulty have this advantage above the 

 other, that they are perspicuously False ; whereas this 

 latter is more mysteriously so . . . because of the hard 

 Words of Congruity and Incongruity." 



Nothing tangible has survived from these earliest 

 discussions, and we begin the subject with Hauksbee, 



' " Encyc. Brit.," 9th edition. 



' Leslie, Tilloch's Phil. Mag., vol. 14, p. 194, 1802. This academy was 

 1" rhaps the first such body devoted to natural science, though it is stated by 



isari and others that da Vinci founded one at Milan. It was active in 

 '< lorence during the years 1657-67. and deserves remembrance for the 

 jiiality of its work. 



' Journal des Sfavans (Amsterdam), November 1768, p. 74. 



* " New Experiments, Physlco-mechanical." (London, 1682.) 

 » [E.g. Hooke.] 



• Hauksbee, " Physico-mechanical Experiments," p. 156. (London, 1709.) 



NO. 2734, VOL. 109] 



whose merit was twofold ; he was an exact experi- 

 menter, and he succeeded in interesting Newton in the 

 problem. His first paper appeared in the Philosophical 

 Transactions for 1709. This led Newton himself to 

 make experiments, and it is a nice question how far 

 the speculations concerning the constitution and inti- 

 mate forces of matter which appear in the incomparable ' 

 thirty-first query are owing to his attention being thus 

 directed to the problem of cohesion. The thirty-first 

 query appeared for the first time in the second edition 

 of the " Opticks " of date 17 18. Be this as it may, 

 though exact experiment and induction begin with 

 Hauksbee, what may be called in eighteenth-century 

 phrase the philosophy of the subject begins with 

 Newton. 



Hauksbee experimented with capillary tubes and 

 also on the rise of fluid between planes of glass, marble, 

 and metal. As fluids he used water, alcohol, and 

 various oils. He noticed that the phenomenon of the 

 rise of fluid in small spaces is not peculiar to one fluid 

 or one solid, and that it is not due to the presence of 

 air, since the rise occurs in a vacuum. His most im- 

 portant experimental result was that the height to 

 which fluid rises is the same in two tubes of the same 

 diameter, but one " at least ten times as thick as the 

 other." Comparing this with the magnet, which can 

 be broken into smaller and smaller pieces each of which 

 will exert the force, he argues that the attraction of 

 the solid for the fluid is limited to the surface of the 

 solid. 



There the matter was allowed to rest so far as the 

 paper of 1709 is concerned. In the paper of 1711 the 

 movements of a drop of oil of oranges between two 

 glass planes inclined to one another at an angle are 

 rightly referred to variations in the area of the surface 

 of contact between fluid and solid, but the statement 

 that the power of attraction must increase in propor- 

 tion to that surface cannot now be defended. His 

 papers of 17 12 and 17 13 are devoted to careful measure- 

 ments of the curves which the surface of water forms 

 when enclosed between glass planes. Brooke Taylor 

 in 1 712 had already pointed out that the curve was an 

 hyperbola. 



There is httle theory in Hauksbee's papers. He 

 was essentially an experimenter,^ but in his book he 

 draws certain definite conclusions from his experiments 

 for which he has not received due credit. 



" That very great Man, Sir Isaac Newton (the 

 Honour of our Nation and Royal Society), has set both 

 these Laws of Attraction in a very clear Light " — 

 namely, that amongst the greater bodies of the universe 

 the attraction decreases reciprocally as " the Squares 

 of the Distances do encrease," and that the smaller 

 portions of matter tend to each other by a law very 

 different and unknown, but one according to which the 

 " attractive Forces do decrease in a greater proportion 

 than that by which the Squares of the Distances do 

 encrease." Hauksbee then goes on to make this 



' " Our Incomparable President," Jurin, 1718. Also Halley wrote con- 

 cerning the " Principia " in 1686, " an incomparable treatise on motion." 



» " There's no other way of Improving Natural Philosophy but by 

 Demonstrations and Conclusions, founded upon Experiments judiciously 

 and accurately made." 



