bridge telescope to search for the planet; but he was anticipated by a Berlin astronomer who followed Leverrier's prediction. Challis actually mapped the planet as a star twice, but had not compared his maps. A great controversy arose; the attitude is neatly expressed by the couplet:
When Challis saw, he couldn't perceive it.
In the early forties there raged in England the "battle of the gauges." Of the railroads built some had adopted a broad gauge (6 feet), some a narrow gauge (4 feet 812 inches). The inconveniences of the diversity were beginning to be felt acutely, and the Government appointed a commission of which Airy was a member. The commissioners reported in favor of the universal use of the narrow gauge; their recommendation was opposed effectively in Parliament by the broad gauge interest, supported by Babbage, who devised very ingenious instruments and made much more scientific observations than Airy. However the narrow guage gradually became the solution of the difficulty. In the fall of 1848 Lord Rosse invited a number of astronomers to his castle at Parsonstown, Ireland, in order that they might inspect his large reflecting telescope. They were entertained for two weeks, Airy and Hamilton were the principal experts. Airy was able to remove a fault in the mounting of the great mirror, for in practical astronomy he was immensely superior to Hamilton; but as a calculator and scientific genius Hamilton was as much superior. It was on this occasion that Hamilton, influenced by Airy's sarcastic remarks, broke his abstinence resolution.
In 1851 Airy presided over the British Association, at the meeting held in Ipswich. The next year he communicated a paper to the Royal Society on the "Eclipses of Agathocles, Thales, and Xerxes." And he also lectured on the subject at the Royal Institution. In 1854 he renewed the attempt to determine by pendulum vibrations the intensity of gravity at the bottom of a mine; this time he chose the Harton coal mine in the north of England, and for his assistants observers
