THE PLANET MARS.

Wairarapa Age, Volume XXXII, Issue 9594, 14 September 1909, Page 7

THE PLANET MARS.

Mars will be nearer the earth next Saturday than it has been since 1892. hence it is not surprising that the planet is now receiving a considerable amount ot attention, especially as there are several large instru • ments available that were not erected in 1894. It was in that year that Professor Percival Lowell inaugurated his observatory at Flagstaff, Arizona, for the special purpose of making a continuous Btudy of Mars under all configurations, and his work there has marked a notable advance in our knowledge of the planet's markings. The site was chosen with great care after many experiments, with a view to securing the btst possible telescopic definition. The observatory is at an altitude of 7,000 ft on the slopes of San Francitico Peak, Arizona, the mountain is ;lothed • with pine and other trees, while it is surrounded by the great American desert, and, it is probable ,hat this combination explains the 'xcellent definition, the dry desert ,jr securing clearness, while the >asis of vegetation protects the jround from overheating, with conlequent unsteadiness. Perhaps the nost important single result obtain>d was the successful photography it the planet, commneced four years »go by Professor Lowell's assist ints, Lampland and Slipher, and repeated with still greater success in I9o7,plates were used that were very jensitive to the red end of the spectrum, and a large number of short jxposures were given, so as to five more opportunity of catching the mome.its of best definition Some of the exposures show one region of the planet well, some show another but the principal ;anais appear on so many aa to eave no doubt of their objective reality and it must be remembered ;bat, before these photographs were taken this was not universally :onceded, some asserting that they were wholly the product of optical llusion. It must be admitted that .he canals as photographed are much iroader and less well defined than as mown in the drawings this is inevitable from the site of the grain )f the plate, and on the whole these photographs greatly increase our :or.fidence in the accuracy of the Jrawings in fact, we can truat these lp to a certain point as correpsondng to actual detail on the planet s, however, questionable whether' Professor Lowell does not press ,hem further in this direction than is eigtimate. Dr G. Johnstone Stoney las reminded us in his recent pam)hlet "Telescopic Vision," that ! iwing to diffraction and interference ;he telescopic image cannot give us in absolutely perfect representation >f the original thus in a microicope, when we press magnifying )Ower beyond what the aperture will warrant, we get spurious mages. Some of the very line letails drawn by Lowell, such as ;he dark spots or "oases" where the :anals cross, or the triangular 'carets," where they leuve the lusky regions for the "deserts," nay be of this spurious character, aid one should aways bear in mind ;he possibility of optical illusion in liscuseing details that are on the 'ery limit of visibility.