At each successive favourable opposition, these strange objects called _canali_ (channels) by their discoverer, but rather misleadingly 'canals' in England and America, were observed by means of all the great telescopes in the world, and their reality and general features became well established.
In Schiaparelli's first map they were represented as being much broader and less sharply defined than he himself and other observers found by later and equally favourable observations that they really were.
_Discovery of the Double Canals._ In 1881 another strange feature was discovered by Schiaparelli, who found that about twenty canals which had previously been seen single were now distinctly double, that is, that they consisted of two parallel lines, equally distinct and either very close together or a considerable distance apart.

This curious appearance was at first thought to be due to some instrumental defect or optical illusion; but as it was soon confirmed by other observers with the best instruments and in widely different localities it became in time accepted as a real phenomenon of the planet's surface.
_Round Spots discovered in_ 1892.
At the favourable opposition of 1892, Mr.W.H.Pickering noticed that besides the 'seas' of various sizes there were numerous very small black spots apparently quite circular and occurring at every intersection or starting-point of the 'canals.' Many of these had been seen by Schiaparelli as larger and ill-defined dark patches, and were termed seas or lakes; but Mr.Pickering's observatory was at Arequipa in Peru, about 8000 feet above the sea, and with such perfect atmospheric conditions as were, in his opinion, equal to a doubling of telescopic aperture.

They were soon detected by other observers, especially by Mr.
Lowell in 1894, who thus wrote of them: "Scattered over the orange-ochre groundwork of the continental regions of the planet, are any number of dark round spots.

How many there may be it is not possible to state, as the better the seeing, the more of them there seem to be.

In spite, however, of their great number, there is no instance of one unconnected with a canal.