Tuesday, 29 January 2013

Biographical musings

This post is cross-posted from the Connecting with Collections blog.

My current project is about King Arthur's Table.  I described this in a previous post.  As I've explained before, it stems from my PhD research into a 14th-century manuscript, The Equatorie of the Planetis.

Yesterday I was in London, looking in the archives of the Royal Institution for information about how and why King Arthur's Table was built according to the instructions in the manuscript.  I didn't find any direct evidence, but I discovered plenty about its creator, Derek Price, and his relationship with Lawrence Bragg, the director of the Cavendish Laboratory where KAT was made.
Derek de Solla Price with a model of the Antikythera Mechanism
I was struck by how many of my research projects have included a strong biographical element.  Maybe it's just the way my research interests push me, or perhaps there's always a biographical aspect to every history.  Either way, I do think personal stories add some human interest.

Price's story is an intriguing one.  I haven't got to the bottom of it, but it seems that for him, coming to Cambridge was a new beginning.  His background was far from prosperous: his father was a tailor and his mother a singer, and he studied for his first degree and doctorate at South West Essex Technical College (part of the University of London).  After taking his doctorate in physics he moved to teach applied mathemetics at the then University of Malaya in Singapore.  This was in 1947, the same year he got married.  But in 1950 something changed.  He decided to change subjects from mathematics and physics to the history of science, and began to make enquiries about studying or working at Cambridge.  This was to lead to his second PhD, for which he researched the Equatorie manuscript he had discovered in the library at Peterhouse.

The archives show that several people in Cambridge were curious, even suspicious, about his reasons for leaving Malaya.  There are hints that he did not fit easily into life in Cambridge.  It's tempting to suppose that this may have had something to do with his social or racial (Jewish) background, but there is no clear evidence on that point.  Either way, it is fascinating to see how, when he decided to make a new start in his career, he was prepared to work incredibly hard to make it happen.

As I've also come to Cambridge a little later in life, it's something I can identify with.  And of course it's been said that a biographer must be able to identify with their subject to some extent.  Is this the beginning of a beautiful biographical relationship?  We'll see.

Thursday, 24 January 2013

What's the difference between an astrolabe and an equatorium?

This is a question I've been asked several times, and it's a reasonable one given that this blog is called "Astrolabes and Stuff", yet I've mainly been posting about equatoria.  So I'm going to answer it in this post.
14th-century astrolabe at the Whipple Museum of the History of Science

First, it's important to stress the one thing astrolabes and equatoria have in common.  They are both tools, calculating devices.  As such, they simplify (and approximate) tasks that could have been done by geometrical calculation - but the astrolabe and equatorium get them done much faster.

So, what are they calculating?  Here's the key difference.  An astrolabe (from the Greek astro-, meaning "star", -labos, meaning "instrument", "measurer", "meter") tracks the stars.  On the other hand the word "equatorium" comes from the Latin √¶quatio, which generally means "correction" rather than "equation", and refers to the correction that needs to be made to convert a planet's mean position to its actual position.  So this is an instrument squarely focused on the planets.

What about the Sun and Moon?  Are they stars or planets?  The answer is of course neither - but also both, in some ways.  This is where we come to the more fundamental difference between astrolabes and equatoria: the timescales on which they operate.

TECHNICAL BIT (feel free to skip this paragraph).  Ancient astronomers noted two kinds of regularity in the planets' motions: tropical and synodic periods.  The tropical period of a planet is the average amount of time it takes to go all the way around the ecliptic (i.e. to travel round all the stars).  The synodic period is the amount of time between periods of retrograde motion.  (For a quick explanation of the significance of retrograde motion, see this post of mine.)

Of all the planets known since antiquity, Saturn takes the longest to go all the way around the ecliptic - to pass all the constellations and end up back where it started.  The 4th-century-BCE astronomer Eudoxus estimated that this tropical period took 30 years; we now say 29.42 years, so he wasn't too far off.  An equatorium has no problem showing this.  Of course there are many ways in which you could say that we require even longer periods of time to be shown - for example, the Greeks adopted the Babylonian idea of great cycles - the amount of time it took before a planet was behaving in the same way at the same place on the ecliptic.  Jupiter's great cycle is 83 years.

Whereas an equatorium tracks planets over years, most of the functions of an astrolabe are best appreciated within a single day, and the information provided by a normal astrolabe repeats after one year.  Here are some of the things it can tell us:
1.  Where a star, or the Sun, will rise on the horizon
2.  How long a star, or the Sun, will stay above the horizon (i.e. the time between rising and setting)
3.  The longitude of the Sun (i.e. its position on the ecliptic) on a given day
Detail of the same astrolabe as above (Wh.1264),
showing the calendar for January/Aquarius,
with various saints' days in the inner circles.
4.  The height of the Sun (or any star) at noon
5.  How long it will take after sunset to get dark (or to get light before sunrise)
6.  The time of day, for a given date
7.  The date, if you observe the Sun at noon, sunrise or sunset
8.  The height of a building, if we know how far away from it we are

There may be many other functions too.  For example, an astrolabe may operate in unequal hours (where there are always 12 hours between sunrise and sunset) as well as equal hours; it may show us the astrological Great Houses, and the calendar on the back may feature a range of saints' days as well as the months and zodiac signs.

Smaller than an astrolabe,
but less likely to work after
being dropped in the bath
This dazzling array of functions means that astrolabes are sometimes compared to Swiss Army knives.  But these days I'm more struck by the comparison to a smartphone.  They are both up-to-date technological items, but more importantly they are both amalgamations of quite a lot of previously existing technology in one easily portable and user-friendly unit.  I suspect they also have in common the fact that despite their enormous range of functions, it tends to be the more basic functions that get/got used most often.

A 20th-century astrologer?
Which brings us to another crucial point: smartphones and astrolabes are both must-have status symbols, valued as much for their visually (and tangibly) attractive design as for their practical functions.  I suppose in a sense smartphones are now too common for the analogy to work perfectly - astrolabes were perhaps more like the earliest mobile phones for the 1980s yuppies - a sign of success, with a faint but perhaps false suggestion of technological know-how.

An equatorium, on the other hand, is a decidedly specialist item.  Its lack of functions - as we've seen in previous posts, it can tell us the longitudes of the Sun, Moon and planets, the latitude of the Moon, but not much else - raises the question of who would want one, and why.

These are very important and hotly debated questions.  I'll return to them in future posts, but for now it's probably fair to say that whereas astrolabes had wide-ranging appeal, equatoria were mainly for people with narrow astrological interests.  Not only did they not tell you as much, but they were harder to use and the theory underpinning them was more complex.

Less attractive equatorium
As a result, they never developed into status symbols in the same way that astrolabes did.  Equatoria could be made shiny and attractive - check out this one at the Museum of the History of Science (MHS) in Oxford - but that was much rarer.  (It's possible that such shiny equatoria were as much demonstrations of the maker's knowledge and skill as items that customers actually wanted.)

Such shininess may account for one key difference between astrolabes and equatoria today: there are way more astrolabes!  There are 182 in the MHS collection, but only a handful of equatoria survive in the whole world.  It's a handy reminder that the survival of objects, and their display in museums today, depends on more than just their significance (however you'd define that).

I'll come back to some of these issues in future posts.  If you are burning to find out more about astrolabes right now, I recommend this excellent site.

Tuesday, 8 January 2013

King Arthur's Table: From Cavendish to Whipple

Remember when I found King Arthur's Round Table?  I told the story way back in my second ever blog post.  Go and have a read if you've not already - it's quite the Indiana Jones adventure.  Or just skip to the summary below...

SUMMARY: Six-foot model of "my" equatorium built for top historian of science Derek de Solla Price in 1950s.  Long lost.  Found but not identified and renamed "King Arthur's Table" by witty cataloguer.  Found in the Whipple stores by me, with help from the curators.

Now I've just started a new project studying this model.  My research will be part of the Connecting with Collections programme run by the University of Cambridge Museums.  It's a six-month research-based internship, and we interns will be blogging as a group here.

So what's the research about?
King Arthur's Table symbolizes a fascinating moment in the history of science and of Cambridge University.  It was built in the Cavendish Laboratory - in the same building, at almost exactly the same time, that Crick and Watson were working on the structure of DNA.  In the same year as that great breakthrough, 1953, Robert S. Whipple died.  He had already made substantial donations to found a new museum and a new university department - History and Philosophy of Science - next door to the Cavendish.

Derek Price was one of the first people to work in the new Whipple Museum.  He was friends with Lawrence Bragg, the youngest-ever Nobel laureate and director of the Cavendish.  The "Table" was made for Price in the Cavendish workshops - a 20th-century replica of a 14th-century instrument that, despite not being "authentic", was destined to hang in the new Museum of the History of Science.

daddy and baby equatoria
Tracing this history, by studying contemporary documents as well as the instrument itself, I reckon I can learn a lot about the glory days of the Cavendish Laboratory, the foundation of the Whipple Museum, and History of Science as a new discipline and university department in the postwar years.  There's also lots to learn about the way museum collections are put together and curated; the way we view the past and its representation today.

Hopefully the "Table" will soon be back on display in the Whipple Museum after a gap of almost exactly 50 years, together with a computer model showing how it works.  In the meantime, I'll be blogging here and on the Connecting with Collections blog as my research progresses.  Check back soon for updates!

Thursday, 3 January 2013


We all miss the Sun at this time of year, don't we?  (Unless you're reading this from Australia, I suppose.)  Luckily for you, this blog post will help you find it!

In case you've forgotten what the sun looks like
In previous posts we've learned how to make and calibrate a planetary equatorium, and how to use it to find the longitude of the planets and Moon.  In my last equatorium post I mentioned latitude for the first time: unlike the planets, the Moon's latitude matters because medieval astronomers were rather keen to be able to predict eclipses.

The manuscript I've been studying mentions just one more use.  (There are one or two functions the author didn't get around to explaining, which I may get around to writing about later.)  We may, of course, want to find out where the Sun is on the ecliptic.  This is the easiest technique of all.

As our manuscript tells us, the Sun "hath non Epicicle ne non Equant": as seen from the Earth, it moves constantly in the same direction against the background of fixed stars throughout the year.  There's just one irregularity: the seasons (as measured between solstices and equinoxes) are not all equal in length).  This was noticed as far back as 330 B.C. by the Greek astronomer Callippus; the lengths of the seasons were first accurately measured around 130 B.C. by Hipparchus.  Hipparchus realised that accounting for this inaccuracy would mean abandoning one of the three basic assumptions about the Sun's motion:
  1. It travels at constant speed...
  2. ...on a circular orbit...
  3. ...which is centred on the Earth.
The easiest principle to abandon was the third: Hipparchus gave the Sun an eccentric (but still circular) orbit.  It's following Hipparchus that I marked a large and slightly eccentric circle on my equatorium, with its centre displaced from the centre of the disc by 1/30th of its radius.  The direction of that displacement (the Sun's aux) moves by about 2° every 100 years; at the end of the fourteenth century, it was at the beginning of Cancer, or 90° as measured from the vernal equinox (the "head of Aries").

Since we already have the Sun's eccentric circle marked on our equatorium, all we have to do is look up its mean motus in our tables.  Regular readers of this blog will know that we use that information to stretch a black thread from the centre of the equatorium to the edge of the face, to where it is marked with the number matching what we've got for the mean motus.

Then we take our white thread and lay it parallel to the black thread, with one end at the centre of the Sun's eccentric circle.  It will be right next to the black thread, since the Sun's orbit is not all that eccentric.  Where the white thread crosses the Sun's eccentric circle is the Sun's true place.  We can measure that by also moving the black thread to that point (to be clear, the threads are no longer parallel but now meet at the Sun's eccentric circle).  The black thread will continue to the edge of the face, where we can read off the Sun's longitude.

That's it - you don't even need to use the big Epicycle! 

Wednesday, 2 January 2013

The Encyglobedia hits the news

In between all the mince pies and playing with my new toys, I had an interesting lesson in media relations last week as a little piece of research I did attracted quite a bit of press attention.

Early on the morning of the 28th, I was barely awake and leafing through The Times as I worked up the energy to go for a run... and was surprised to come across this little item on page 24:

That report was based on a little research project I did for my master's last year (summarised here on the Whipple Museum website).

It got better: a longish article (with my name!) in The Independent, a "big picture" feature on the BBC News website, articles in a bunch of other papers including the Irish Independent and the Belfast Telegraph, and even being called an "expert"! (OK, that was in the Cambridge News.)

Even more exciting was when I was contacted by two descendants of the globe's maker, a man who I'd been able to find almost nothing about.  They had read the story in a Spanish newspaper (possibly this one) and contacted me through this blog to share what they know of their (great) grandfather. One of them even has a very similar globe that he made!  I'm still looking into the leads they gave me, and hope to blog soon about what I find.

How did all this come about?  Well, to cut a long story short, the lovely PR people at Cambridge were looking for some research to feature in their Research Horizons magazine.  My investigation into this globe was nicely self-contained, had some very pretty pictures, and provided some well timed publicity for the Whipple's new globes gallery.  So my research got written up into a little article for the Cambridge University website, with a short accompanying film:

Even after all this (and even when I heard that the Press Association had shown interest in the story), I didn't expect it to spread so widely.  Frankly, I didn't see how "The World Inside a Spanish Globe" was news.  But I hadn't foreseen the "angle" that most newspapers went with: the idea that the globe represents an interactive style of education, which we tend to think of as a modern innovation.  This was something that I had touched on in my research, but only tentatively; I am very interested in education (I used to be a teacher) but know little about its history, particularly in Spain.  Most of the contemporary sources I'd read were educational philosophy - I didn't have much hard evidence about how that philosophy was put into practice.  And above all, I'm not certain that the globe was used in a school - it could equally likely have been an expensive toy for a wealthy family (though in that setting it would still have been educational, especially since many children were home-schooled).

So overall I would say that the reports did distort my research slightly, but not to an unreasonable extent.  And in hindsight it's easy to see why there was so much interest.  Here's four things I've learned; you might find them useful if you too want to be interviewed on local radio!

1.  A short, simple bit of research (like my six-week master's project) is easily summarised in a 400-word newspaper article, especially when it takes a case study approach, as my work did.
2.  And research that comes accompanied by pretty pictures is always going to be attractive.
3.  If there's a way the research can be spun so it has a topical message, it will sell well.
4.  Most importantly, if you want your research to spread widely, publicise it in a slow news week!  With nothing else to report but the Queen's speech and the content of the New Year's Honours, the way was clear for my "encyglobedia" (a name that provoked decidedly mixed reactions, by the way).

Happy New Year!