Aquae Sulis

Just time for a quick post this lunchtime, in between a whole day of meetings with students about projects and other things. This afternoon I have to whizz off to the fine city of Bath where this evening I am giving a public lecture jointly organized  by the University of Bath and the William Herschel Society (which is based in Bath).

The title of my talk is The Cosmic Web, and a brief outline is as follows.

The lecture will focus on the large scale structure of the Universe and the ideas that physicists are weaving together to explain how it came to be the way it is.

Over the last few decades astronomers have revealed that our cosmos is not only vast in scale – at least 14 billion light years in radius – but also exceedingly complex in texture, with galaxies and clusters of galaxies linked together in immense chains and sheets tracing out an immense network of structures we call the Cosmic Web.

Cosmologists have developed theoretical explanations for its origin that involve such exotic concepts as ‘dark matter’ and ‘cosmic inflation’, producing a cosmic web of ideas that is in many ways as rich and fascinating as the Universe itself.

The University of Bath website has more details of the talk, and I think they are going to do a podcast too. I’ll actually be doing a recap in a couple of weeks’ time in Bristol at an event for the Institute of Physics, of which more anon.

Bath is only about an hour from Cardiff by train and I’m very much looking forward to this trip as I have never been to the University of Bath before.I remember from my schooldays that the Romans named the place Aquae Sulis (or, as my Latin teacher Mr Keating who couldn’t pronounce his esses would say, Aquae Thulith).  The local waters were famous for their healing powers even before the Romans got to England, and the Celtic inhabitants attributed this to a deity they called  Sulis. The Romans kept the name, although they decided that Sulis was actually their goddess Minerva in disguise. The Romans were good at appropriating local traditions like that.

The only potential fly in the ointment is the British weather, which has been terrible over the last week or so and further deluges are forecast this afternoon and evening. As I write, though, it’s actually fine and sunny and the weather map suggests the worst of the current band of rain has passed to the north of here. I hope I’m not tempting providence, and that there won’t be too much of the aquae heading in my direction!

20 Responses to “Aquae Sulis”

  1. Rhodri Evans Says:

    Be sure to point us towards the podcast when you get back. Hope it goes well!

  2. Anton Garrett Says:

    Herschel lived in Bath for a decade and it is at that time that he first came to attention as an astronomer, as told in one of the chapters of the deservedly lauded recent book “The age of wonder: How the Romantic generation discovered the beauty and terror of science” by Richard Holmes.

  3. Bryn Jones Says:

    I visited the Cosmos and Culture exhibition at the Science Museum in London last week, which was moderately interesting. Among the exhibits were a Herschel telescope that is probably the one he used in the discovery of Uranus from the back garden of his house in Bath, a Herschel glass prism which is probably the one he used in the discovery of infrared radiation (from Slough), and a poster for a performance of Handel’s Messiah in Bath which he himself conducted and in which Caroline Herschel was a soloist.

  4. Mr Physicist Says:

    Bath tis a fine city and I have visited the University on a number of occasions – it has a very good public lecture series. Hope the “Cosmic Web” was well received.

  5. Rhodri Evans Says:

    I suspect the prism is not the original as that is in Bath and I’ve been trying to get hold of it to do some experiments with it. So far they’ve refused to release it.

  6. Rhodri Evans Says:

    One of the most interesting things about the Herschel prism is why on Earth a glass prism transmitted in the infrared at all as glass is opaque in that part of the spectrum. I’m hoping to head up an experiment to measure the prism’s transmission properties for the first time. At the moment the Herschel museum is refusing to release it….

  7. telescoper Says:

    I was talking with various people over dinner after the lecture and apparently there is a plan to measure the infrared transmission properties of the prism, using facilities in the labs at Cardiff. The Herschel museum is not allowing it to be taken away at the moment, however, for what seems to be some reason connected with insurance and liability if it gets lost. In my opinion the prism is more likely to be a decorative item than a true optical device.

  8. […] In the Dark A blog about the Universe, and all that surrounds it « Aquae Sulis […]

  9. Rhodri Evans Says:

    Peter -measuring the prism is the project i’m talking about. It was my idea in the first place to do it and to use the Fourier Transform Spectrograph in Cardiff to do it. At the moment the Herschel museum is saying no to releasing it but I’m not giving up. I have a backup plan 🙂

  10. Bryn Jones Says:

    I can’t recall where the Science Museum got the Herschel prism from: which collection it was borrowed from or whether it was from their own collections. The prism might have been on loan from the Herschel museum. It is possible that there is more than one Herschel prism around which is claimed to be the one he used in the experiment in which he discovered infrared radiation.

  11. Rhodri Evans Says:

    Actually the Science museum owns the prism and it’s on loan from them to the Herschel museum. Part of my backup plan is to now approach the Science museum.

  12. Rhodri Evans Says:

    Another intriguing thing about the prism is that it looks like and probably was part of a chandalier. Where did Herschel get it from? Where was it made and why not use a normal prism. In 1800 he wouldn’t have had a chandalier in his house as he wasn’t rich enough at that point in his life. If you read the original discovery paper it’s clear he set up his control thermometer quite a distance from the end of the visible spectrum.

  13. I’m not familiar enough with chandaliers to comment on how similar chandalier glass is to Herschel’s prism, but it does seem plausible that he might have reused some existing piece of glass. The prism is an unusual shape: it is very long. The cross section is an equilateral triangle, if I remember correctly.

    Do I remember reading that Newton bought the prisms for his original experiment from a stall at a fair which was selling them as toys/novelty items?

  14. Rhodri Evans Says:

    Well in 1800 Herschel probably couldn’t afford to have a prism made by one of the many quality opticians in Britain, so where he got the chandalier piece from is a mystery. Yes, it is an equilateral cross section with a small glass ball at each end. I have a photo of it somewhere which we could post here Peter?

  15. My thinking about William Herschel is somewhat different. He was very highly skilled at grinding and polishing metal-alloy telescope mirrors, and also had experience of grinding lenses. He certainly could have ground glass prisms had he wanted to do so (and for all I know, he may have done so at some other time).

    Might it have been simpler for him to recycle some old glass of the correct shape than to grind his own prism? It would have saved a lot of work.

  16. Rhodri Evans Says:

    Yes it certainly would have been easier to use a suitable piece of glass than to make his own. I need to find out Herschel’s lens making abilities.

  17. From memory, Herschel did experiment with lens grinding during his optical experiments in the 1770s, before switching his main attention to mirror grinding. He used small, sometimes very small, lenses in the eyepieces of all his reflecting telescopes, which I believe he manufactured himself.

  18. Bryn Jones Says:

    Perhaps one note might be of interest to general readers of this page: the two volumes of J. L. E. Dreyer’s collection of Sir William Herschel’s scientific papers can be found at the Internet Archive at

  19. […] evening I realised I could actually use it in a new post inspired by a nice email I got after my Herschel lecture in Bath. More of that in a minute, but first the couple of paras I edited from the chaos […]

  20. […] a podcast of which is available here. It doesn’t seem like a whole year has passed since I blogged about that […]

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