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Antoniadi dissolves the canals at Meudon

Four nights before opposition, the 83-centimetre Meudon refractor showed Antoniadi a Mars crowded with irregular detail and not one straight line.

A very large refracting telescope painted pale mint green, inside a dome lined with wooden planking between dark iron ribs. Its long closed tube runs diagonally up to a wide objective cell near the top of the frame, crossing a horizontal box girder with heavy dark fittings at each end that spans the width of the picture. The whole assembly stands on a tall cast column pierced by rectangular openings, rising from a bare observing floor ringed with dark railings.
The Grande Lunette at Meudon Observatory, a double refractor carrying an 83-centimetre visual objective and a 62-centimetre photographic one on a single tube, and the largest refracting telescope in Europe in 1909. Antoniadi had his first night at its eyepiece on 20 September of that year; the photograph dates from 2015. · Image: Serge Golovanow

On 20 September 1909, four nights before a favourable opposition, Eugène Antoniadi got his first night on the Grande Lunette at Meudon, an 83-centimetre refractor and the largest refractor in Europe. The air was steadier than anything he would see again through that instrument. Mars was covered in detail, none of it geometric. There were no canals at all.

The planet, he wrote, "appeared covered with a vast and incredible amount of detail held steadily, all natural and logical, irregular and chequered, from which geometry was conspicuous by its complete absence." Where Lowell's maps ran a clean line, Antoniadi saw a broken chain of unrelated dark patches that the eye, at lower resolution, would connect. On 19 October he drew Mars again in ordinary seeing, and several canals came back, one pair of them neatly doubled. He kept that drawing as evidence too. The canals, he concluded, were a product of poor seeing.

Antoniadi was Greek, had worked as Camille Flammarion's assistant at Juvisy, directed the British Astronomical Association's Mars Section, and had drawn canals himself in the 1890s. Six years earlier, Joseph Evans and Edward Maunder at Greenwich had reported in Monthly Notices that schoolboys shown discs of scattered dots would reliably draw lines between them.

Percival Lowell went on publishing until his death in 1916, and the canals survived in popular atlases, encyclopaedia entries and schoolroom astronomy for another half-century. Observers were still reporting them in the 1950s, and a defender could always argue that the seeing had been poor, the observer's eye untrained, or the canals seasonal. Mariner 4's twenty-one frames in July 1965 showed craters and no network. Mariner 9 mapped 85% of Mars in 1971–72 and found volcanoes, a canyon system 4,000 kilometres long, and dry channels carved by water that had stopped flowing billions of years earlier, almost none of them along the lines Schiaparelli had drawn. Antoniadi's La Planète Mars, published in 1930, remained the standard reference until spacecraft replaced it.