Indian signallers operating a heliograph, 1935

Photograph, India, North-West Frontier, 1935.

The heliograph used a mirror to reflect sunlight to a distant observer. By moving the mirror, flashes of likght could be used to send Morse code. It was an ideal tool in the mountainous wilderness of the North-West Frontier of India as it allowed long distance communication without a fixed infrastructure.

From an album of 387 photographs compiled by Captain (later Major) Wynne Howes-Roberts, 1st Battalion 13th Frontier Force Rifles, 1935.