The Extractor at Kelder Street

The referral came through a GP, which is not how most of them come. The occupier was thirty-four, in good health, and had been sleeping in the front room for nine months because he could not sleep in the bedroom. He described a pressure in the hall, nausea when he stood still in it, a persistent sense of being watched from the bedroom doorway, and on four occasions in the year, a figure at the foot of the bed which he described as grey and about the height of the door handle when seen from lying down.

He had already worked out that he did not believe in ghosts. He was not asking us to tell him that. He was asking us why it was still happening.

What is above a takeaway

The flat sits over a restaurant kitchen. The kitchen has a extraction canopy discharging through a duct that rises in a boxed void against the party wall, passes within 15 cm of the hall floor structure, and terminates above the roofline. The duct was installed in 1996 and, at the time of the survey, was carried on two steel brackets bolted directly to a joist, with no resilient mounts of any kind.

We measured the hall for four hours with the restaurant trading and two hours after it closed.

Nineteen hertz

The frequency matters because of a paper. In 1998 an engineer named Vic Tandy, working in a medical equipment laboratory, wrote up his own haunting: a grey figure in the periphery of his vision, a cold sweat, a feeling of being watched, all of it in one room. He found a 19 Hz standing wave from an extractor fan whose mounting had failed. He fixed the fan and the room stopped. The paper is The Ghost in the Machine, published in the Journal of the Society for Psychical Research in 1998, and it is worth reading in the original rather than in the version the internet has made of it. The Survey's own note on the file is that the figure most often quoted online is 19 Hz and the figure in the paper is not exactly that, which tells you how many of the people repeating it have read it.

Two things about 19 Hz. It is below the frequency most people hear as a tone, so it arrives as sensation rather than sound. And it sits close enough to a commonly quoted resonance of the human eye that Tandy suggested the grey figure was the observer's own eyeball being driven — a mechanism which is plausible, frequently repeated, and has never been demonstrated cleanly by anybody since.

The recommendation

Two resilient mounts and a 600 mm section of flexible duct, fitted at the point where the rigid run passes the hall floor. The Survey costed it at £61 in parts and put it in writing to the freeholder, with a copy to the occupier and the GP.

The work was not done. The freeholder disputed responsibility, then disputed the survey, then stopped replying. The occupier gave notice in January and moved to his sister's.

What this file is here for

Most of the archive looks like this one, and the Survey files the boring outcome with the same care as the other kind, because the boring outcome is the reason anybody should believe the other kind when it turns up.

But it is also here because of the last line of the operator's note. The Survey's business is establishing causes. It has never been able to do anything at all about the fact that establishing a cause does not switch the experience off. A man who knows the fan is a fan still stands in his hallway at two in the morning and feels somebody behind him, because the mechanism is in his body and not in his opinions.

We do not have an instrument for that part and we have stopped pretending the problem is the instrument.