ON COHESION. 483 



materially concerned. The well known experiment, of the two exhausted 

 hemispheres of Magdeburg, affords a still more striking instance of appa- 

 rent cohesion derived from atmospherical pressure ; and if we place between 

 them a thick ring of elastic gum, we may represent the natural equilibrium 

 between the forces of cohesion and of repulsion ; for the ring would resist 

 any small additional pressure with the same force as would be required 

 for separating the hemispheres so far as to allow it to expand in an equal 

 degree : and at a certain point the ring would expand no more ; the air 

 would be admitted, and the cohesion destroyed, in the same manner as 

 when a solid of any kind is torn asunder. But all suppositions founded on 

 these analogies must be considered as merely conjectural ; and our know- 

 ledge of every thing which relates to the intimate constitution of matter, 

 partly from the intricacy of the subject, and partly for want of sufficient 

 experiments, is at present in a state of great uncertainty and imperfection. 

 One of the most powerful agents, in changing and modifying the forms 

 of matter, is the operation of heat, by which the states of solidity, liquidity, 

 and elastic fluidity are often produced in succession ; and the investigation 

 of the nature and effects of heat will constitute the subject of the two next 

 lectures. 



LECT. L. ADDITIONAL AUTHORITIES. 



Cohesion in general. Desaguliers on the Cohesion of Lead, Ph. Tr. 1725, p. 345. 

 Hambergus, De Cohesione, 4to, Jena, 1732. Winckler, De Causis Conjunctionis, 

 4to, Leipz. 1736. Felice, do. 4to, 1757. 



Capillary Action. Fabri, Dialogi Physici, Lyons, 1669. Boyle, Ph. Tr. 1676, 



?. 775. Hauksbee on the Effect of Capillary Tubes remaining in a Vacuum, ibid. 

 706, p. 2223; on Different Points, ibid. 1709, p. 258 ; 1711, p. 395; 1712, pp. 413, 

 539 ; 1713, p. 151. Taylor on the Ascent of Water between Two Plates, ibid. 1712, 

 p. 538 ; on Attraction of Wood to Water, ibid. 1721, p. 204. Jurin, ibid. 1718, 

 p. 739; 1719, p. 1083. Bulfinger, Com. Petr. ii. 233, iii. 281. Musschenbroek, 

 Diss. Phys. pp. 271, 334. Clairaut, Fig. de la Terre, 1743. GeUert on Melted Lead 

 in Tubes, Com. Petr. xii. 293 ; on Prismatic Tubes, ibid. xii. 302. Segner on the 

 Surfaces of Fluids, Com. Gott. 1751, i. 301. Tetens, De Fluxu Siphonis in Vacuo, 

 4to, Biitzow, 1763. Lalande, sur la Cause de 1'Elevation des Liqueurs, 12mo, Par. 

 1770. Morveau on the Attraction of Water and Oils, Jour, de Phy. i. 172, 460. 

 Lord C. Cavendish's Table of the Depression of Mercury, Ph. Tr. 1776, p. 382. 

 Achard on the Adherence of Solids to Fluids, Hist, et Mem. de Berlin, 1776, p. 149. 

 Schriften, i. 355. Dutour, Jour, de Physique, xi. 127, xiii. Supp. 357, xiv. 216, 

 xv. 46, 234, xvi. 85, xix. 137, 287. Besile, ibid, xxviii. 171, xxix. 287, 339, xxx. 

 125. Monge on Apparent Attractions and Repulsions, Hist, et Mem. 1787, p. 506, 

 Nich. Jour. iii. 269. Bennet, Manch. Mem. iii. 116. Leslie, Ph. Mag. xiv. 193. 

 Young on the Cohesion of Fluids, Ph. Tr. 1805, p. 65. Laplace, Mec. Cel. Sup- 

 plem., and Bullet, de la Soc. Philom. 1819, p. 122. Edin. Encyc. art. Capillary 

 Attraction. Gauss, Principia Generalia Theorise Figurse Fluid, in Statu ^Equilib. 

 Gott. 1830. Poisson, Mem. de 1'Acad. ix. Theorie de 1' Action CapUlaire, 4to, 

 1831. Link, Pogg. Annalen, 1832, xxv. 270, xxvii. 193, xxix. 404. 



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