Robert Williams Wood (May 2, 1868 – August 11, 1955) was an American physicist and inventor who made pivotal contributions to the field of optics.

Wood's patents and theoretical work inform modern understanding of the physics of ultraviolet light, and made possible myriad uses of UV fluorescence which became popular after World War I.

However, he decided to study optics instead when he witnessed a rare glowing aurora one night and believed the effect to be caused by "invisible rays".

In his pursuit to find these "invisible rays", Wood studied and earned several degrees in physics from Harvard University and the Massachusetts Institute of Technology.

[citation needed] As a student at Harvard he swallowed marijuana as part of a self experiment, recorded the hallucinations he experienced in a report for a course of psychology.

[6][7] In early 1900 he visited the United Kingdom giving a lecture at the Society of Arts in London on the diffraction process of photography in colours.

The French physicist Prosper-René Blondlot claimed to have discovered a new form of radiation similar to X-rays, which he named N-rays.

[15] In 1909, Wood constructed the first practical liquid mirror astronomical telescope, by spinning mercury to form a paraboloidal shape, and investigated its benefits and limitations.

[11] His investigations into the "Candy-Box Murder", a 1930 bombing that killed 18-year Naomi Hall Brady and two of her siblings at her home in Seat Pleasant, Maryland, helped convict her brother-in-law Leroy of manslaughter.

[11][17] The bizarre death of 51-year-old socialite Katherine Briscoe at her Baltimore home in 1934 from a carelessly discarded blasting cap and his experiments derived therefrom would lead to the first scientific publication on explosively formed penetrators in the Proceedings of the Royal Society in 1936.

[22] She was his "constant companion for more than 60 years, although she herself had no interest in scientific things" , in Baltimore, at their summer place near Easthampton on Long Island, and during their travels abroad.

[22] Although physical optics and spectroscopy were Wood's main areas of study, he made substantial contributions to the field of ultrasound as well.

While in Langevin's lab, he observed that high-powered ultrasonic waves can cause the formation of air bubbles in water, and that fish would be killed or an experimenter's hand would suffer searing pain if placed in the path of an intense sound beam.

The experimental setup was driven by a two kW oscillator that had been designed for a furnace, allowing for the generation of very high output power.

When attempting to take the temperature of the mound of erupting oil with a glass thermometer, Wood and Loomis accidentally discovered another set of effects.

Even if very fine thread of glass only 0.2 millimetres (0.01 in) in diameter and 1 metre (3 ft 3 in) long was put in the oil at one end, holding a bulge in the glass at the other end still resulted in a groove being left in the skin and the skin being seared, with painful and bloody blisters forming that lasted several weeks, showing that the transmitted ultrasound vibrations generated were quite powerful.

[25] Wood and Loomis also investigated the formation of emulsions and fogs, crystallization and nucleation, chemical reactions, interference patterns, and standing waves in solids and liquids under high-intensity ultrasound.