It’s the International Year of Light, and what better way to commemorate it than by recreating the experiment which led William Herschel to infrared radiation. Our very own Jim Stone, from the Department of Physics was asked to reconstruct Herschel’s experiment for a three part BBC 4 series entitled “Colour: The spectrum of science” airing on November 18th. Check out his diary of the day here: colour: the spectrum of science

“The experiment would take place in the Herschel museum, or more specifically, in the kitchen. I’m not sure what I really expected from the crew as we met bleary eyed that morning (we started at 6am) to set up. With hindsight, obviously a cameraman and sound recordist who make their livings out of optics and acoustics are going to be curious and quite capable when it comes to physics. Especially on a science documentary.

"Herschel had made his infrared discovery when he noticed the coloured optical filters he was using to observe sunlight seemed to also pass different amounts of heat. He wondered if different colours had different temperatures so using a prism to disperse sunlight, he laid out several thermometers in the spectrum and a control one just outside the red edge. It was the unexpected result of the control thermometer showing the largest change that lead Herschel to conclude that there was light beyond the red edge of the spectrum which we could not see.

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"Back in 2015, and under very creative direction, the kitchen was set up as it would have been when in the late eighteenth century. Windows were blocked out and beeswax candles were lit, then, on the table in the centre, the brilliant beam of white light emerging from the supercontinuum (we modernised the sunlight source somewhat) and striking a prism sending a bright spectrum across the table to a series of neatly laid out thermometers looked fantastic. With everything now ready the sound recordist muttered the words everyone was longing to hear, “fancy a bacon sandwich?”

"After breakfast our presenter arrived. I rather naively thought someone would have scripted everything, but no, “I’m going to need a few minutes to work out what to say” says UCL physicist Helen Czersky, and then straight into filming.

"I have no idea how long we spent there, I think I left my perception of time fast asleep in bed that morning. Different shots, different angles, different lines all looking and sounding great. As we were getting the last few gratuitously arty shots we were given the nod to pack up in time for the museum opening. Soon all the equipment was cleared and eighteenth century kitchenware again occupied the space.

"Emerging from our supercontinuum/candle light illuminated Georgian time warp into the midday sun felt dreamlike, but I also felt very satisfied. If the series is half as good as it seemed it would be to me that day then it will be well worth watching."

Let us know in the comments below if you watch Jim, and make sure you check out the rest of the series too - starting on 4 November.

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