The application of the law of the transformation and conservation of energy to the operations of the voice is nicely illustrated by the well-known candle-flame test of (supposedly) breath-control. To perform this test the singer is instructed to practise the exercises for breath-control while holding a lighted candle with the flame an inch or two in front of the lips. According to the idea of the breath-control advocates, the expired breath should escape so slowly, and with so little force, that no current of air can be detected at the lips, the expiration therefore does not cause the candle flame to flicker. Describing the toneless breathing exercises to be practised with the candle flame, Browne and Behnke say, "Let it be observed that the above exercise is quite distinct from the well-known practice of _singing_ before a lighted candle, which is, comparatively speaking, an easy matter." (_Voice, Song, and Speech_.) A very striking fact is stated correctly by Browne and Behnke,--there is no current of air created at the lips during tone-production. Of the truth of this statement the reader may readily convince himself by trying this same experiment with a candle flame, or even with a lighted match. Hold a lighted match just in front of the lips and sing a powerful tone. The quality of the tone is of no consequence so long as it be powerful. Just sing, shout, yell, the louder the better. You will find that the flame is less affected under these circumstances than by the quiet expiration of ordinary breathing. Considerable practice and close attention are required in order to hold back the breath in toneless breathing exercises. Whereas in producing any kind of powerful tone the breath normally creates no current of air at the lips. There is no reason for considering this experiment a test of correct tone-production. It is impossible to produce a powerful tone of any kind, good, bad, or indifferent, and at the same time to create an appreciable current of air at the lips. Needless to say, the breath-control theorists have entirely failed to grasp the significance of the candle-flame experiment. Yet we have here a demonstration of the mechanical law of tone-production. Considered as a mechanical process, tone-production occurs when the energy exerted by the expiratory muscles, in their contraction, is converted into energy of motion of the vocal cords.[8] In other words, tone-production is an example of the transformation of energy. The law of the transformation and conservation of energy must therefore apply to this operation. This law is stated as follows: "Energy may be transformed from any of its forms to any other form. When energy is thus transformed the quantity of energy in the resulting form or forms is equal to the quantity of energy in the original form."