Originally published: London : Printed for J. Murray, 1780.

Although first to suggest the possibility of light frequencies beyond the visible spectrum, the natural philosopher John Elliott (1747-87) was better known at his death for his failed suicide in front of the woman he loved. Tried for attempting to shoot her, he was acquitted but died in prison awaiting trial on the lesser charge of assault. First published in 1780, this work was his most important. Contemporary science held that vibrations of the air were directly communicated to the optic and auditory nerves and passed on to the sensorium, while Elliot proposed, through experimentation upon himself, the existence of sensory receptors, each tuned to only a limited part of the spectrum of physical frequencies. This insight led him to postulate the existence of what we now know to be ultraviolet and infrared radiation, thus paving the way for further discoveries in human sensory perception.