Hertz's Spark

Plate 18 speaks for itself: “Light, without the light.”

The Physics

Hertz made sparks in one circuit and detected sparks in a separate loop across the room, showing that electromagnetic waves exist and travel like light, as Maxwell predicted.

c = 1 / √(μ₀ ε₀)

• c: speed of light in vacuum, m s⁻¹
• μ₀: vacuum permeability, N A⁻²
• ε₀: vacuum permittivity, F m⁻¹

c = 299 792 458 m/s (exact). Karlsruhe, 1886–88.

Sources

• H. Hertz, Ann. Phys. 270, 551 (1888).
• SI Brochure, 9th ed. (2019): exact c.

On the poster

Plate 018, “Hertz's Spark”: the pixel-art plate with its slogan “Light, without the light.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.