CONTENTS. xxi 



LECTURE XXXIII. 

 ON HARMONICS, 304. 



Theory of harmonics; Combinations of sounds, 304. Beats, 305. Grave 

 harmonics ; Concords ; Melody ; Rhythm ; Simple compositions, 306. Diatonic 

 scale ; Half notes or semitones, 307. Minor mode ; Discords ; Rules of accom- 

 paniment, 308. Temperament ; Distinction of the notes, 309. 



LECTURE XXXIV. 

 ON MUSICAL INSTRUMENTS, 310. 



Division of musical instruments, 310. Harp; Lyre; Harpsichord; Spinet; 

 Pianoforte; Dulcimer; Clavichord; Guitar, 31 L Violins of different kinds; 

 Vielle ; Trumpet Marigni ; Aeolian harp ; Human voice, 312. Drum ; Stacada, 

 313. Bell; Harmonica; Vox humana pipe; Simple wind instruments; Mixed 

 wind instruments, 314. History of Music ; Lyre; Hermes; Terpander; Pytha- 

 goras; Simonides; Tibia; Aristotle, 315. Ctesibius; Pope Gregory; Guido; 

 Bacon ; Galileo ; Mersenne ; Kircher ; Meibomius ; Wallis ; Newton, 316^ 

 Brook Taylor ; Sauveur ; Lagrange ; Euler ; Bernoulli ; Dalembert ; Sounds of 

 rods ; Grave harmonics of Romieu and Tartini ; Sounds of pipes, 317. Chladni; 

 Laplace, 318. Chronological table, 319. 



LECTURE XXXV. 

 ON THE THEORY OF OPTICS, 320. 



Importance of optics; Division of the subject; Definition of light; Ray of 

 light, 320. Motion of light; Homogeneous mediums; Reflection; Refraction, 

 321. Polished surfaces, 322. Return of a ray; Refractive density: Index of 

 refractive power, 323. Intermediate refraction ; Total reflection ; Dioptrics and 

 catoptrics; Focus, 324. Plane speculum; Principal focus; Convergence by 

 reflection; Concave and convex mirrors, 325. Prism; Multiplying glass ; Lens; 

 Effects of lenses ; Focus of a lens, 326. Joint focus ; Image ; Optical centre ; 

 Curvature of the image, 327. 



LECTURE XXXVI. 



ON OPTICAL INSTRUMENTS, 328. 



Divergence of light, 328. Photometers ; Measurement of refractive densities; 

 Instruments strictly optical ; Images formed by lenses and mirrors, 329. Mag- 

 nifiers; Simple microscopes; Globules; Illumination of an image; Burning 

 glasses, 330. Materials of lenses and mirrors ; Images visible in every direction ; 

 Camera obscura, 331. Solar microscope, 332. Lucernal microscope; Phantas- 

 magoria, 333. Astronomical telescope ; Double microscope ; Galilean telescope ; 

 Common day telescope; Dr. Herschel's telescope, 334;' Newtonian reflector; 

 Gregorian telescope; Cassegrain's telescope; Smith's microscope; Curvature of 

 images in telescopes, 335. Magnifying powers of telescopes ; Field glass ; Dou- 

 ble magnifier, 336. Aberration from colour ; Achromatic glasses ; Achromatic 

 eye piece ; Micrometers, 337. Divided speculum, 338. 



