GKVBRAL CONSIDERATIONS 



HEARING. 

 PHYSIOLOGICAL ASPECT OP ACOUSTICS. 



A|>|Mtr*tua for determining the conditions 



I. Of the audibility of sounds. 



'2. Of the perception of the distinction of sounds. 



M. Of the harmony or discord of simultaneous sounds. 



4. Of the melodious succession of sounds. 



5. Of the timbre of sounds, and of the distinction of vowel sounds. 



6. Of the time required for the perception of the sensation of sound. 



RADIATION. 

 PHYSICAL ASPECT OP OPTICS. 



1. Sources of Radiation. Heated bodies, solid, liquid, and gaseous. 

 Solid. Heated by a blow-pipe as in the oxy-hydrogen limelight. 



Heated by their own combustion, as in the magnesium light 



and glowing coals. 

 Heated by an electric current, as the carbon electrodes of 



the electric lamp. 

 Heated by concentrated radiation from other sources, as in 



the phenomenon called Calescence. 

 Liquid, as in hot fused metals and other bodies. 

 Gaseous. Heated by their own combustion, as in flames. 



Heated by a Bunsen burner, as the sodium light. 

 Heated by the voltaic arc. 

 Heated by the induction spark. 



J. Distributors. Burning mirrors and lenses, condensing lenses for solar 

 microscopes, magic lanterns, &c., lighthouse apparatus ; telescopes, 

 microscopes, &c. 



M. Selectors. Absorbing media and coloured bodies in general, prisms 

 and spectroscopes, ruled gratings, &c. : tourmalines, Nicol's prisms, 

 and other polarizers. 



