INDUSTRIAL LABOUR 449 



Thus the tenor expends less energy, for equal range and dis- 

 tinctness of articulation, than the baritone or the bass voice. 

 Generally a speaker will exceed the minimum values given above, 

 since he has to make himself easily heard to all his audience. 

 Careful articulation increases the effective range of the voice. 



If men, women and children are compared, it is found that, for 

 the same effect, women tire four times less than men, because their 

 vocal cords are shorter. The advantage is greater still in children, 

 who, as every one knows, talk with an extraordinary volubility. 



The limits of the human voice are : 



Bass. F! to F 3 equivalent to 174 to 696 simple vibrations. 



Tenor. C 2 to C 4 ,, 261 to 1,044 



Alto F 2 to F 4 348 to 1,392 



Soprano C 3 to C 4 522 to 1,044 



The limits of auditory perception correspond to a minimum 

 sonorous intensity acting on a plane at right angles to the path of 

 the sound waves. The ear is most sensible to sounds having a 

 frequency of about 500 vibrations per second. This means an 

 expenditure of energy of about one hundred thousandth of 

 an erg per second per square centimetre. This quantity of energy 

 is so minute that one kilogrammetre would sustain the sound for 

 many thousand years. The sensation of the persistence of a sound 

 sung after it has actually ceased is the more marked the lower 

 the note. The acoustic properties of large halls depend on their 

 cubic contents and the absorption caused by the walls, the fur- 

 niture and the audience itself. The best result? are attained when 

 the period of resonance lies between J and | of a second. If the 

 capacity of a hall is C, the absorption of the vvalls A, and N the 

 number of persons present. The duration of the resonance T 

 can be obtained from the following equation : 



17 C 

 " 44 N + A 



The fatigue experienced by a speaker depends therefore on 

 several variable qualities, some of which are unknown. 



339. The Expenditure of Energy in Speaking. The expenditure 

 of energy by a speaker or a vocalist can only be measured by a 

 color imetric chamber similar to that of Atwater and Benedict. 

 The respiratory valve which is employed in other cases to measure 

 the consumption cannot be easily employed in this case, as it 

 obstructs fiee vocalisation. The results of an experiment made 

 with this apparatus, with a valve adjusted to the mouth by a 

 large rubber membrane, may, however, be given. 



The subject was 30 years of age, and weighed 69 kg. When at 

 rest the following results were obtained ; - 



