XVlll 



CONTENTS. 



human voice'; 40{T. Drum ; Stacada ; Bell ; Harmo- 

 nica; Vox humana pipe ; 401. Simple wind instru- 

 ments; Mixed wind instruments; 402. History of 

 music; Lyre; Hermes ; Terpander; Pythagoras; Si- 

 raonides;403. Tibia; Aristotle; Ctesibius; Pope 

 Gregory; 404. Guido; Bacon ; Galileo ; Mersennc ; 

 Kircher ; Meibomius ; Wallis ; Newton ; Brook Tay- 

 lor ; Sauveur; 405. Lagrange; Euler; Bernoulli; 

 Dalembert; Sounds of rods; Grave harmonics of 

 Romieu and Tartini ; Sounds of pipes. Chladni ; 406 . 

 Laplace; Chronological table ; 407. 



Lecture xxxv. On the theory of 

 optics ; 408. 



Importance of optics ; Division of tlie subject ; De- 

 finition of light ; 408. Ray of light ; Motion of light . 

 Homogeneous mediums ; 409. Reflection ; 410. Re- 

 fraction ; 411. Polished surfaces ; Return of a ray ; 

 Refractive density ; 412. Index of refractive power ; 

 Intermediate refraction; Total reflection; 413. Di- 

 optrics and catoptrics ; Focus ; 414. Plane speculum ; 

 Principal focus; Convergence by reflection ; 415. Con- 

 cave and convex mirrors ; Prism; Multiplying glass; 

 Lens; 416. Effects of lenses ; Focus of a lens; 41T. 

 Joint focus; Image ; Optical centre ; 418. Curvature 

 of the image; 419. 



Lecture xxxvi. On optical instru- 

 ments ; 420. 



Divergence of light; Photometers ; 420. Measure- 

 ment of refractive densities; Instruments strictly 

 optical ; 421. Images formed by lenses and mirrors ; 

 Magnifiers ; Simple microscopes ; Globules ; 429. Il- 

 lumination of an image ; Burning Glasses ; Materials 

 of lenses and mirrors ; 423. Images visible in every 

 direction; Camera obscura; 424. Solar microscope ; 

 425. Lucernal microscope : Phantasmagoria ; 426. 

 Astronomical telescope ; Double microscope ; 427. 

 Galilean telescope : Common day telescope ; Dr. 

 Herschel's telescope; 428. Newtonian reflector;, 

 Gregorian telescope ; Cassegrain's telescope ; Smith's 

 microscope; Curvature of images in telescopes, 129; 

 Magnifying powers of telescopes ; Field glass ; 430. 

 Double magnifier; Aberration from colour; Achro- 

 matic glasses; 431. Achromatic eyepiece; Micro- 

 meters ; 432. Divided speculum ; 433. 



Lecture xxxvi. On physical optics; 

 434. 



Sources of light; Combustion ; Slow decomposition; 

 434. Electricity ; Friction ; Solar phosphori ; 435. 

 Emission'of light; Velocity of light ; Apparent aber- 

 ration ; 436. Oblique reflection ; Diffraction ; Dis- 

 persion ; Colour; 437. Division of the spectrum; 

 Light of diff'erent kinds; 438. Mixed lights ; Imita- 

 tion of white light ; Primitive colours ; 439. Mixture 

 of colours by rapid motion; Combinations ; 440. At- 

 mospherical refraction; Horizontal refraction; 441. 

 Rainbows ; 442. Halos and parhelia ; 443. Refrac- 

 tion of ice ; Complicated halos ; 444. Double refrac- 

 tion; Iceland spar; Second refraction ; Transparent 

 plates ; 445, 446. 



Lecture xxxviii. On vision ; 447. 



Description of the eye ; 447. Image on the retin* j 

 Advantages of the arrangement ; 448. Inversion of 

 the image ; Instinct ; 449. Sensibility of the retina ; 

 Focus of the eye ; Accommodation ; 450. Change in 

 the crystalline lens ; Uses of the iris ; 451. Optome- 

 ter ; Myopic and presbyopic sight ; 452. Single 

 vision ; Judgment of distance ; 453. Apparent mag- 

 nitudes of the sun and moon ; Aerial perspective ; 

 Painting; 454. Panorama; Duration of sensations; 

 Ocular spectra ; 455, 456. 



Lecture xxxix. On the nature of 

 light and colours; 457. 



Theories respecting the nature of light ; 457. Sim- 

 ple propagation ; Transparent mediums; 458. Uni- 

 formity of velocity ; 459. Reflection and refraction ; 

 Partial reflection ; 460. Total reflection; 461. Sources 

 of light ; Aberration ; Double refraction ; 462. 

 Dispersion ; Colours of thin plates; 463. Alternate 

 union and extinction of colours; Light admitted by 

 two holes ; 464. Supposed dimensions of undulations ;. 

 Correction ; Stripes in a shadow ; 465. Light passing 

 through a narrow aperture; Colours of striated sur- 

 faces; 466. Curved stripes.af colours; Fringes near 

 a shadow ; 467. Colours of thin plates ; 468. Co- 

 lours of natural bodies ; 469. Colours of mixed plates ; 

 supernumerary rainbows ; 470. Colours of concave 

 mirrors ; Agreement of the Iluygenian theory with 

 the phenomena ; 471. 



Lecture xl. On the history of 

 optics ; 472. 



Knowledge of the ancients ; Empedocles ; 472^ 



