Even when the back is turned toward the flame the sonorous pulses run round the body, reach the tube, and call forth the song. A pitch-pipe, or any other instrument which yields a note of the proper height, produces the same effect. Mounting a series of tubes, capable of emitting all the notes of the gamut, over suitable flames, with an instrument sufficiently powerful, and from a distance of 20 or 30 yards, a musician, by running over the scale, might call forth all the notes in succession, the whole series of flames finally joining in the song. When a silent flame, capable of being excited in the manner here described, is looked at in a moving mirror, it produces there a continuous band of light. Nothing can be more beautiful than the sudden breaking up of this band into a string of richly-luminous pearls at the instant the voice is pitched to the proper note. One singing flame may be caused to effect the musical ignition of another. Before you are two small flames, _f′_ and _f_, Fig. 118 (p. 273), the tube over _f′_ being 10-1/2 inches, that over _f_ 12 inches long. The shorter tube is clasped by a paper slider, _s_. The flame _f′_ is now singing, but the flame _f_, in the longer tube, is silent. I raise the paper slider which surrounds _f′_, so as to lengthen the tube, and on approaching the pitch of the tube surrounding _f_, that flame sings. The experiment may be varied by making _f_ the singing flame and _f′_ the silent one at starting. Raising the telescopic slider, a point is soon attained where the flame _f′_ commences its song. In this way one flame may excite another through considerable distances. It is also possible to silence the singing flame by the proper management of the voice. SENSITIVE NAKED FLAMES § 7. _Discovery of Sensitive Flames by Le Conte_