DISCOVERY 



301 



Madler had obser\-ed and delineated the crater under 

 a totally different aspect, as had also Schmidt himself. 

 This observation, confirmed by other astronomers, 

 was followed by the equally startling announcement 

 by Klein, of Cologne, in 1879, of the formation of a 

 new crater. 



Nevertheless, the majority of astronomers adhered 

 to Madler 's view. Nasmyth and Carpenter, in their 

 classical work on The Moon, expressed " the strong 

 belief that no vestige of its former volcanic activity 

 lingers on the moon — that it assumed its final condition 

 an inconceivable number of ages ago " ; while con- 

 ceding that " minute changes of a non-volcanic char- 

 acter may be proceeding in the moon, arising from the 

 \-iolent alternations of temperature to which the sur- 

 face is exposed during the lunar day and night." 

 Flammarion, forty years ago, was as a voice crying 

 in the wilderness. Referring to the darkening of the 

 floor of the great walled-plain Plato with the progress 

 of the lunar day, he expressed the view that " the 

 odds are ninety-nine to one that it is not the light 

 which produces the effect, and that it is the solar 

 heat. ... It is highly probable that this periodical 

 change of tint on the circular plain of Plato, visible 

 everj' month to any attentive observer, is due to a 

 modification of a vegetable nature, produced by the 

 temperature." 



The work of Schmidt was carried forward bj' a num- 

 ber of painstaking English amateurs, chief among 

 whom was the late Mr. T. G. Elger, of Bedford. In 

 1S95 Elger published his reasoned conclusions in a 

 balanced and cautious way in his volume on The Moon. 

 His standpoint represented a reaction from the view 

 of Madler and from the much more extreme version 

 of that view given in so many textbooks. " The 

 knowledge we possess," he wrote, " even of the larger 

 and more prominent objects, is far too slight to justify 

 us in maintaining that changes which on earth we should 

 use a strong adjective to describe have not taken 

 place in connection with some of them in recent years." 

 Elger hmiself inclined to belief in change. Referring 

 to the var\-ing tints of some of the level regions, he 

 cautiously remarked : "It has been attempted to 

 account for these phenomena by supposing the exis- 

 tence of some kind of vegetation, but as this involves 

 the presence of an atmosphere, the idea hardly finds 

 favour at the present time, though perhaps the possi- 

 bility of plant growth in the low-hdng districts, where 

 a gaseous medium mav prevail, is not altogether so 

 chimerical a notion as to be unworthy of consider- 

 ation." He stated, however, his strong conviction 

 of the need of further intensive study, maintaining 

 that only by confining attention to selected areas 

 of hmited extent, and by studying every visible 

 object under all conditions of illumination, could 



progress be made. " A complete photographic survey 

 of a few selected regions as a basis for an equally 

 thorough and exhaustive scrutiny by direct observa- 

 tion would, it is believed, lead to a much more satis- 

 factory and hopeful method for intimately furnishing 

 irrefragable testimony as to permanency or change 

 than any that has been undertaken." 



Elger died in 1897 ; three years later his suggestion 

 was put into practice by Professor W. H. Pickering, of 

 Harvard, who since the beginning of the centur}' has 

 had the field of lunar astronomy practically to himself. 

 On August 12, 1892, an occultation of Jupiter was 

 observed by Pickering at Arequipa, in Peru, and the 

 slight flattening of the disc was attributed by him 

 to refraction in a lunar atmosphere of extreme tenuity. 

 His observations of the crater Linne during the next 

 few years confirmed him in the belief that the moon 

 was by no means destitute of change. In 1899 an 

 expedition to Jamaica convinced him of the excellence 

 of its climate for the photographic and visual study 

 of the moon, and in 1900 the Harvard astronomical 

 station Wcis erected at Mandeville, a convenient 

 point in the island. The photographs of the lunai 

 surface taken during the following year formed the 

 basis of the large atlas, containing many plates and 

 descriptive matter, which was published towards the 

 close of 1903 under the title of The Moon. 



Pickering was not the first to apply photography 

 to the lunar surface. At the Lick Observatory a 

 large altas was commenced, but the project was dis- 

 continued. At the Paris Observatory Loewy and 

 Puiseux obtained many beautiful photographs ; while 

 Weinek, of Prague, formed an atlas combining many 

 Paris and Lick photographs. But the amassing of 

 large numbers of isolated photographs is in itself 

 insufficient to settle the vexed question of change, 

 or, indeed, to add much to our knowledge of the moon. 

 Pickering was the first investigator to carry out the 

 idea of Elger — photography of a few selected regions 

 as a basis for an exhaustive scrutiny by direct observa- 

 tion. The idea has been justified by the progress of 

 selenography since the beginning of the century. 

 Indeed, there has been developed what Pickering him- 

 self calls the " new selenography " — " the seleno- 

 graphy which consists not in a mere mapping of cold 

 dead rocks and isolated craters, but in a study of the 

 daily alterations that take place on small selected 

 regions— changes that cannot be explained by shifting 

 shadows or varying hbrations of the lunar surface." 



A close study of these "small selected regions" 

 convinced Pickering as early as 1902 that the con- 

 ventional view of the moon as an absolutely dead world 

 was untenable. He had concluded ten years earlier 

 that a very thin atmosphere does exist, with a density 

 probably not e.xceeding one ten-thousandth part 



