Light is a wave
Maxwell expressed Faraday's lines of force as equations. When he used them to calculate the speed of electromagnetic waves, the answer came out almost exactly equal to the speed of light. The conclusion was bold: light is an electromagnetic wave, and other, invisible waves must exist too.
From equations to Wi-Fi
Maxwell's waves were proven in the laboratory more than 20 years later by Heinrich Hertz. Today they underpin Radio, Wi-Fi, mobile networks, GPS and the microwave oven. Every engineer who designs an antenna works with Maxwell's equations.
The first colour photo
In 1861 he had a ribbon photographed three times, through red, green and blue filters, and projected the three images through the same filters onto one screen. The result was a colour image. Building up an image from the three colours red, green and blue is still how the sensors in cameras and displays work today.