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Some of Edison's inventions have a character at present of little more than picturesque playfulness, such as the Phonograph, perhaps the most remarkable of these minor inventions; the Aerophone, by which sounds are amplified without loss of distinctness; the Megaphone, an instrument which, inserted in the ear, so magnifies sounds that faint whispers may be heard a thousand feet; the Phonometer, for measuring the force of the soundwaves caused by the human voice; the Microtasimeter, for measuring small variations in temperature.

So it is only necessary to twist the phonometer about on its pivot until the sound is received most loudly in the horns and the band of light is greatest.

Banging and pounding, we forged ahead, straining our eyes to watch the road, the distance, the time, and the phonometer all at once.

The sound enters the two horns of the phonometer, is focused at the neck, and strikes on a delicate diaphragm, behind which is a needle.

Without the phonometer to warn us, it must inevitably have met us and blocked our escape over the road ahead.