542 HISTORY OF SCIENCE. 



investigator of our own time to discover the physical causes of the 

 consonances, discords, and qualities of tones. It has been by bringing 

 to the task great mathematical acquirements, rare experimental skill, 

 a profound knowledge of physiology, and something of the inspiration 

 of genius, that Helmholtz has succeeded in 



Untwisting all the chains that tie 

 The hidden soul of harmony. 



HERMANN Louis HELMHOLTZ was born in 1821, and was educated 

 for the medical profession. He has been Professor of Physiology at 

 Konigsberg, Heidelberg, and Berlin successively. As an a'id to the 

 study of physiology, Helmholtz turned his attention to physics, and 

 as necessary to the mastery of physics he devoted some time to mathe- 

 matics. In each of these three great departments of science he has 

 distinguished himself by his original researches. The works by which 

 he is well known throughout Europe are "The Conservation of Force," 

 1847 ; "A Manual of Physiological Optics," 1856 ; "The Sensations 

 of Tone as a basis for the Physiological Theory of Music," 1862. 



The reader doubtless understands that just as a disturbance at any 

 point on the surface of a still piece of water raises a wave which ex- 

 pands in an ever-widening circle, so a sound-wave spreads from its 

 point of origin through the air in all directions as an enlarging sphere. 

 But there is this essential difference : the free surface of the water rises 

 into ridges and sinks into hollows, whereas there is no unoccupied 

 place into which the disturbed particles of the air can move. They 

 are therefore impelled towards the contiguous particles, and there the 

 air is condensed until its elasticity reacts in repelling the particles 

 and producing a corresponding rarefaction. Thus the ridges and 

 troughs of water-waves would correspond respectively to spherical 

 shells of condensation and rarefaction in air-waves. That different 

 systems of waves may simultaneously and independently traverse a 

 piece of water is a matter of every-day observation, which may help us 

 to understand the like independence of innumerable systems of sound- 

 waves moving at the same time through the same mass of air. It is 

 the frequency of the vibrations which determines fat pitch of any tone, 

 and their amplitude, i.e., the amount of compression and rarefaction 

 which determines its loudness. There is a third property of musical 

 tones, the cause of which was a mystery until Helmholtz's masterly 

 investigations cleared it up. When the same note is sung with the 

 same loudness on different vowel sounds, a very different tone is 

 heard; or, again, when the same vowel is sung in the same pitch, the 

 voice of the singer is distinguishable by the quality of the tone. Again, 

 the difference of character in the sound given out by the several 

 musical instruments is readily distinguished by the most careless 

 listener, so that if an air be performed on an unseen instrument, he 

 recognizes the notes of a flute, clarinet, accordion, or trumpet, as the 

 case may be. 



