A Discovery and a Scandal

      

      Explaining 
      Uranus turned out to be a tricky problem of orbital mechanics. Start with 
      the errors in Uranus's predicted motion. Subtract the effects of Saturn 
      and Jupiter. Now examine the remaining, slight irregularities in Uranus's 
      motion. That's all you have left to determine exactly which direction the 
      disturbance is coming from, how distant it is, and how massive it is. And 
      since it's a planet, you have to find a moving target. Hardly an easy problem. 
      Some mathematicians thought it impossible, and no one would tackle it.
      
 Fortunately for our story, two mathematicians did manage to solve it, 
        quite independently of each other, and without knowing the other was working 
        on the problem. John Couch Adams began working on the problem after he 
        graduated from Cambridge in 1843. 
      
 As 
        a starting point for the solution, Adams assumed the planet was at a distance 
        of 38.4 astronomical units, twice that of Uranus. It was also close to 
        the distance calculated by Bode's Law, a curious mathematical sequence 
        that seemed to match -- and potentially predict -- the distances of the 
        planets from the Sun. 
      
 However, the solution Adams devised went unheeded by the Astronomer 
        Royal at the Greenwich Observatory, George Airy, who believed the problem 
        was mathematically unsolvable. Adams refined and resubmitted his prediction, 
        but to no avail.
      
 On the continent, Urbain Leverrier began working on the same problem 
        in June of 1845 and presented his prediction to the Paris Academy of Sciences 
        a year later. Realizing his colleagues had no intention of actually looking 
        for this planet, Leverrier sent his information to Airy at the Greenwich 
        Observatory. Upon comparing the predictions of Adams and Leverrier, Airy 
        decided that Adams's work must have merit, but he never mentioned this 
        to Adams, nor did he inform Leverrier about Adams's predictions, or even 
        about the existence of John Adams, who had beat Leverrier to the solution 
        by eight months.
      
 Though 
        a search was finally begun in July, 1846 at the Cambridge Observatory, 
        the astronomer in charge decided to ignore the predicted location of the 
        planet and conducted a sweeping, rather than a pinpoint, search. Mathematics, 
        after all, was no way to find a planet.
      
 In August, 1846, Leverrier presented another paper in which he gave 
        all the details of the planet -- the orbital elements, mass, and position. 
        He was lauded for his mathematical skills, but no one offered to look 
        for his planet. Frustrated, Leverrier finally sent his predictions to 
        Johann Galle, an assistant at the Berlin Observatory. 
      
 On September 23, 1846, Galle received Leverrier's letter. That night 
        he and a graduate student, Heinrich d'Arrest, aimed their telescope at 
        the predicted location. Within an hour they found the planet. In a triumph 
        of mathematical theory, Neptune had been discovered.
      
 This was rather a scandal for the British, who had been in possession 
        of the necessary information for the discovery, but had failed to act. 
        Leverrier was credited with the discovery, since it was his data the Germans 
        used to find Neptune. When the British tried to stake their claim in this 
        momentous discovery, the Paris Academy of Sciences was in an uproar. Accusations 
        were hurled across the Channel and public denouncements became ugly. Eventually 
        the dispute settled down and, as his contribution became clear, Adams 
        received his due credit. He now takes his place in history beside Leverrier 
        as the first person to predict Neptune's location.
      
 
      
 
Still One Little Problem

      The presence 
      of Neptune now accounted for those errors in the orbit of Uranus -- almost. 
      When all known factors -- including Neptune -- were taken into account, 
      Uranus's motion still had very minor discrepancies from what was predicted. 
      
 This time no one questioned Newton's Law, which had held up rather well 
        over the years. Instead, astronomers proposed another planet as the culprit. 
        Unfortunately, it would be too distant, too dim, and just too difficult 
        to find. The nights at the telescope were long and cold enough already 
        without engaging in a fruitless search, so most astronomers just never 
        tried to find the ninth planet.
      
 
      

        Next: Percival Lowell's Quest
        
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