My revered teacher, Manuel Garcia, opposed, as I have long done, the attack of tone with the open glottis, which results in an outpouring of breath, without bringing the vocal cords into action. Unfortunately, this new system has found swift acceptance. Strange aberration! Garcia, in order to make clear to some of his pupils, who were rather slow of comprehension, the closing, or rather, the drawing together of the glottis, was wont to make them strike the desired tone, holding a lighted candle before them. When the light was extinguished by the attack, this proved that the glottis was open; when closed, the light burned steadily.
Marchesi, Mathilde. Ten singing lessons. Vol. 1. Harper, 1901.