CONTENTS. xxv 



LECTURE XLIX. 



ON THE ESSENTIAL PROPERTIES OF MATTER, 464. 

 Importance of minute objects; Definition of matter, 464. Place of the investiga- 

 tion ; Essential and accidental properties of matter ; Extension ; Divisibility, 

 465. Actual division of matter, 466. Impenetrability, 467. Permeability; 

 Orders of substances ; Repulsion ; Apparent contact, 468. Laws of repulsion, 

 469. Dalton's hypothesis ; Repulsion of liquids and solids ; Reciprocality of 

 repulsion ; Inertia, 470. Gravitation ; Cause of gravitation ; Mathematical con- 

 ceptions, 471. Newton's opinion ; Constitution of a medium capable of pro- 

 ducing gravitation, 472. Difficulties, 473. 



hits 



LECTURE L. 

 ON COHESION, 473. 



Accidental properties of matter; Laws of cohesion; Modification of cohesion 

 by heat, 474. Liquidity; Superficial cohesion, 475. Bubbles; Form of the surface 

 of a fluid, 476. Magnitude of the force of cohesion ; Ascent between two plates; 

 Capillary tubes, 477. Horizontal surface ; Detached portion of a liquid ; Lyco- 

 podium ; Attractions and repulsions of floating bodies, 478. Apparent cohesion 

 of plates ; Drop between plates ; Oil spreading on water ; Sponge ; Long column 

 supported by cohesion, 479. Cohesion of solids; More perfect union ; Solidity; 

 Cause of solidity, 480. Elasticity, 481. Stiffness ; Strength ; Softness ; Ductility; 

 Primary cause of cohesion, 482, 483. 



. . 



LECTURE LI. 



.ill 

 ON THE SOURCES AND EFFECTS OF HEAT, 484. 



Division of the subject of heat; Definition of heat and cold; Excitement of 

 heat; Condensation, 484. Friction; Count Rumford's experiments, 485. 

 Effect of velocity; Pictet's experiments; Heat from combustion, 486. Com- 

 munication of heat; Conducting powers; Fluids, 487. Radiation of heat; Mr. 

 Leslie's discoveries ; Differences of solar and culinary heat, 488. Invisible heat; 

 Equilibrium of radiant heat ; Apparent reflection of cold, 489. Refrangibility of 

 heat; Blackening rays, 490. Effects of heat; Temporary effects ; Expansion of 

 gases; Condensation; Expansion of fluids, 491. Diminution of cohesive powers; 

 Boiling; Slow evaporation ; Contraction, 492. Freezing; Expansion of solids ; 

 Liquefaction, 493. Cracks from heat ; Permanent effects of heat ; Glass drops ; 

 Tempering of metals, 494, 495. 



: plli 



LECTURE LII. 



ON THE MEASURES AND THE NATURE OF HEAT, 496. 

 Measures of expansion ; Pyrometer ; Scale of heat ; Mixtures ; Sun's rays, 

 496. Expansion of solids and fluids; Thermometers; Wedgwood's thermo- 

 meter, 497. Different scales ; Temporary change of a thermometer ; Air ther- 

 mometers, 498. Capacities for heat ; Natural zero, 499. Theory of capacities ; 

 Chemical effects, 500. Latent heat; Mr. Davy's experiments ; Intimate nature of 

 heat ; Theory of caloric, 501 . Confutation ; Heat a quality ; Newton's opinion ; 



