Portrait of Paul-Émile Lecoq de Boisbaudran

Adapted from ⁠an image (public domain), via Wikimedia Commons.

1838–1912

Paul-Émile Lecoq de Boisbaudran

Discovered three elements between 1875 and 1886.

Elements

Lecoq de Boisbaudran found gallium as two new violet lines in a spectrum. Every element has its own lines, as helium's show here.

Emission spectrum

A fingerprint made of light

In 1868, astronomers watching a solar eclipse saw a yellow line at 587.6 nm that matched no element known on Earth. It was named helium, after Helios, the Greek word for the Sun, and wasn’t found on Earth until 1895.

Electrons race through the tube and crash into helium atoms, knocking the atoms’ own electrons up to higher energy levels. As those fall back, the atoms give off light only at the exact wavelengths below, so each gas glows its own colour.

The five gases’ visible lines side by side: each pattern is a fingerprint. Choose one to see it in detail below.

Wavelength in nanometresA nanometre (nm) is a billionth of a metre. Our eyes see light from about 380 nm (violet) to 750 nm (red); a human hair is about 80,000 nm wide.
Helium spectral lines

Click a line to see where it comes from.

388.9 nmviolet

An electron falls from the 3p level down to the 2s level. It loses 3.19 eV of energyAn electronvolt (eV) is a tiny unit of energy used for atoms: the energy one electron gains crossing 1 volt. A particle of visible light carries between about 1.7 eV (red) and 3.3 eV (violet). and gives it off as one particle of violet light. Bigger drops give bluer light.

Energy3p · 23.01 eV2s · 19.82 eV0 eV · ground

The strongest visible lines of neutral helium from the NIST Atomic Spectra Database. Line brightness follows NIST’s relative intensities, which only compare lines of the same element. Colours are approximate, and lamp colours are as they look to the eye.

Keep exploring

Where the dates and stories on this page come from; each event on the timeline links to its own source. Britannica gives 18 April 1838; 1836 appears in some records.