I don't suppose that many patients on this morning's list for an MRI scan at the Mater know that the physics that underpins it all was first formulated by the man who grew up in this house, round the corner in Adela Street. It was to this house that Hugh and Hannah Larmor brought their young family in 1863 or 1864 from the farm at Ballycarrickamaddy in the townland of Magheragall. And it was from here that their eldest child, Joseph, went first to the National School in Eglinton Street (now buried beneath the West Link) and from there, in 1869, to Inst., a fifteen minute walk away.

Two years later, the fourteen-year old matriculated at Queen's College, graduating BA in 1875 and being admitted MA the following year.

It was from here too, that Joseph Larmor set out on a journey of the mind that would bring him, 30 years on, to the recognition that time, the time that Newton held to be absolute, true and mathematical, was nothing of the kind. Rather it depended on the frame of reference of who was telling it. It was a realisation out of its time, for it would take another eight years before Einstein proclaimed the relativity of time as a universal truth.

We are here this morning to commemorate the life and work of a great mathematical physicist in the tradition of his countrymen MacCullagh and Hamilton, Stokes and Thomson and FitzGerald. I couldn't but be struck that this is the 114th blue plaque to be put up by the Ulster History Circle honouring all manner of men and women. Now while we can look at the pictures of Paul Henry and Larmor's near contemporary, John Lavery at the Ulster Museum and recite bits of Louis MacNeice's poems (To this day I remember learning Bagpipe Music at school:…It's no go the Yogi man, it's no go Blavatsky, All I want is a bank balance and a bit of skirt in a taxi); and while some of us are old enough to have driven one of Harry Ferguson's tractors and heard Rinty Monaghan singing after he'd knocked out the best in the world, saying what mathematicians do isn't easy at the best of times. Saying what Joseph Larmor did is harder than most. For two reasons.

One is that his work was concerned with something called the aether. Like the great Maxwell and James MacCullagh, a Tyrone man, Larmor held that everything to do with electromagnetism-that's just a grander word for the plain old electricity and magnetism we learned at school-- happened in this aether. Now the aether isn't easy to pin down. Worse still, there wasn't one aether but several. What was key to Larmor's was that his aether was the source of electric charges that from about 1894 he called electrons, even though electrons, as we know them, weren't identified until 1897. Anyway these electrons were the key that led Larmor to propose that the molecules that made up matter are held together by electrical forces.

The second reason why it's not that easy to get a grip on what Larmor did, is the man himself-- he wasn't a great communicator, spoken or written. Here he is, lecturing on electrodynamics this very morning at Cambridge a hundred years to the day: November 26, 1909:

"….. If we wish to go the bottom of things we want to know how this transmission of power (in an electric circuit) occurs, this enquiry leads us to the aether. The transmission takes place in the aether surrounding the wire itself with a velocity nearly equal to that of light. The aether does it so rapidly as to be almost instantaneous. The conducting wire is merely a guide (there is no elasticity of the aether in the wire itself). It is very much like the transmission of waves in the aether with a cylindrical hole (occupied by the wire). The increased freedom owing to the absence of elasticity is what induces the current to go along the wire. The electrons have greater freedom of motion if the wire is present. The idea that currents go by diffusion was at first merely a hypothesis but is not now so, on the modern electron theory….."

All through the 1890s, Larmor worked out his theory. His results were put together in Aether and Matter (1900). It wasn't a best-seller, though you can still pick up a copy on the AbeBooks website. Don't be fooled by their sales pitch: "An excellent read…a book to enjoy-- a great gift for the reader in your life." Take my word for it, if you're minded to put it on your Christmas list, the reader in your life won't be in your life for long! Aether and Matter is as impenetrable as the day it was written.

Impenetrable it may be, but there on page 174, you'll find Larmor's ground-breaking result, a relation that he was forced to because he needed to connect how different observers record electromagnetic effects. What it amounts to is this: if a moving observer tells the time and compares this with the time read by the observer who's actually holding the clock, then, to the moving observer, the clock appears to be going slow. Now I'm not going to attempt to say how Larmor got to this. You remember how St.Augustine got round the question What is time? " If no one asks of me, I know. If I have to explain to him who asks, I know not." I'm with St. Augustine!

Now here's the rub. The formulae that Larmor wrote down in 1897 are known not as the Larmor transformation but as the Lorentz transformation. Lorentz of Leiden re-discovered them in 1904, seven years after Larmor and a year before Einstein conjured them out of his relativity hat. So, how come Lorentz and not Larmor? Well, Lorentz was the world No. 1 of theoretical physics in his day. He was everything that Larmor was not. He wrote clearly, he travelled widely, he was fluent in German, the lingua franca of physics a century ago. He was revered even by the irreverent Grade III Clerk in the Bern Patent Office, Albert Einstein. When told that FitzGerald in Dublin had scooped him with his science-fiction proposition that moving rods contract, Lorentz fell over backwards to acknowledge FitzGerald's priority.

That's what makes it all the stranger that he didn't concede Larmor's priority over their transformations. There was no lack of cordiality between them. They corresponded from around 1905, when Larmor had become Secretary to the Royal Society. They had met when Lorentz came to London. But in the preface to his own great work, The Theory of Electrons (1909), Lorentz writes "….no space could be spared for the important share in the development of the theory taken by Larmor". I have to say I find that a weethin' disingenuous in a book running to over 300 pages.

I think too that Larmor felt overshadowed by Lorentz. Far from feeling hard done by, he wrote later that the transformations were rightly named for Lorentz. I can't help contrasting this with the virulent campaign waged by the greatest of his predecessors in the Lucasian Chair, Sir Isaac Newton, in his attempts to discredit Leibnitz (over his claim for priority in discovering calculus). Larmor is diffident to a fault. Indeed in their correspondence there is a deference underlying the formality. Here's Larmor writing to Lorentz in 1920, responding to an invitation to a Solway Conference (gatherings of Nobel laureates and " near-Nobelists"): "I fear it would be only as a learner that I could attend." In another letter he writes "….you are so much the best qualified to succeed in this" and later, "I cannot hope ever to assimilate now the difficult four dimensional calculus." This from the Lucasian Professor of Mathematics of the day, no less.

You'll see from your invitation that Larmor's other contributions have not been forgotten. Far from it. He has a theorem, a formula, a frequency and a length, all named after him. You could say the sun never sets on mentions of this length, the Larmor radius, in plasma and fusion laboratories all round the world. He was the first to propose a magnetic theory of sunspots. He was first to show a clear understanding of how radio waves propagate. St. John's College, Cambridge has a Larmor Lecture. Neither is he forgotten here at home. He is a Freeman of the City, Queen's offers Larmor studentships. Inst. remembers him through Larmor House. And now we have this splendid blue plaque that folk passing by can look up at and I hope be curious enough to ask what he did.

What of the man himself? Would he have approved? Well, maybe not! When Cambridge wanted to put on a celebration in his honour, he would have none of it. But there are times when a great man or woman needs to be remembered in spite of themseves. Larmor is a man of the North, worthy of the honour we have done him; an outstanding mathematical physicist from the Ulster tradition in the line of James MacCullagh, William Thomson, Alfred Robb and in our own time, John Bell.

Joseph Larmor sits with them.

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