1 8 SCIENTIFIC APPARATUS. 



In the physiological treatment of Optics, only those radiations 

 are considered which excite in us the sensation of Light, though 

 other radiations can be detected and studied by their thermal, 

 chemical, and even mechanical effects. 



VIBRATIONS AND WAVES. 

 PHYSICAL ASPECT OF ACOUSTICS. 



i. Sources. Vibrations of various bodies. 



Air Organ pipes, resonators and other wind instru- 

 ments. 



Reed instruments. 

 The Siren. 



Strings .-..'. Harp, &c. 

 Membranes . . Drum, &c. 

 Plates . . . Gong, &c. 

 Rods . .<.'"-''' Tuning-fork, &c. 

 2. Distributors. Air . Speaking tubes, stethoscopes, 



&c. 



Wood, Sounding rods 

 Metal, Wires. 

 3. Pugging of floors, &c. 



4. Reservoirs. Resonators, Organ Pipes, Sounding-boards. 

 5. Dampers of pianofortes. 

 6. Regulators. Organ Swell. 

 7. Detectors, the ear; Sensitive Flames, Membranes, 



Phonautographs, &c. 

 c. Tuning-forks, pitch-pipes, and musical scales. 



HEARING. 



PHYSIOLOGICAL ASPECT OF ACOUSTICS. 

 Apparatus for determining the conditions 

 i. Of the audibility of sounds. 

 2. Of the perception of the distinction of sounds. 



