At first, Le Verrier rejected Adams's results. In 1856, Plana admitted Adams's conclusions, claiming to have revised his own analysis and arrived at the same results. However, he soon recanted, publishing a third result different both from Adams's and Plana's own earlier work. Delaunay in 1859 calculated the fourth-order term and duplicated Adams's result leading Adams to publish his own calculations for the fifth, sixth and seventh-order terms. Adams now calculated that only 5.7" of the observed 11" was accounted for by gravitational effects. Later that year, Philippe Gustave Doulcet, Comte de Pontécoulant published a claim that the tangential force could have no effect though Peter Andreas Hansen, who seems to have cast himself in the role of arbitrator, declared that the burden of proof rested on Pontécoulant, while lamenting the need to discover a further effect to account for the balance. Much of the controversy centred around the convergence of the power series expansion used and, in 1860, Adams duplicated his results without using a power series. Sir John Lubbock also duplicated Adams's results and Plana finally concurred. Adams's view was ultimately accepted and further developed, winning him the Gold Medal of the Royal Astronomical Society in 1866. The unexplained drift is now known to be due to tidal acceleration.