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SCIENCE. 



[N. S. Vol. IX. No. 227. 



of 18 inches aperture and 315i inches focal 

 length. The magnifying powers used were 

 commonly 440 and 617 ; an eye-piece of 

 power 820 served for the micrometric meas- 

 urements. Among the auxiliary instru- 

 ments we mention an Arago polariscope, 

 which has been employed, perhaps for the 

 first time, upon Mars by W. H. Pickering 

 at Flagstaff ; also a scale of very fine lines 

 of different sizes, which served for the com- 

 parison and estimation of the size and in- 

 tensity of the lines observed on the planet. 



The very numerous and varied observa- 

 tions which form the contents of the pres- 

 ent volume have led to many results, the 

 most important of which have been an- 

 nounced by Mr. Lowell in his book ' Mars, ' 

 published in 1895. That book contains 

 many discussions and theories of great in- 

 terest as to the physical constitution of the 

 planet and its atmosphere, its habitability, 

 and as to the most plausible manner of ex- 

 plaining the curious phenomena which have 

 been observed. The substance of those re- 

 searches and of those discussions has been 

 reproduced in the present volume. The 

 readers of Science have been made familiar 

 with them by the critical analysis of them 

 given by Professor W. W. Campbell in 

 the number for August 21, 1896. I have, 

 therefore, not occupied myself with the 

 theoretical and hypothetical portions, and 

 I am able to confine myself to the observa- 

 tions. In view of their great variety, I 

 shall be obliged to limit myself to the con- 

 sideration of some of the more character- 

 istic points. 



First, as to the polar spots and their 

 periodic variations, which are known to be 

 analogous to those of our polar snows. 

 The manner of development of the polar 

 caps and the phases of their increase are 

 entirely unknown, and it is probable that 

 they will always remain so ; for during the 

 period of their increase they are for the 

 most part or wholly enveloped in the night 



of the pole. But the process of their dis- 

 solution can be followed without much difii- 

 culty when the inclination of the planet's 

 equator with respect to our line of vision 

 approaches the maximum value possible, 

 which occurred in 1894. As for that, the 

 observers at Flagstaff have been able to 

 study the phenomena of the southern spot 

 from the beginning of June, when its di- 

 ameter was about 55°, up to its total (or 

 nearly total) destruction, which occurred 

 toward the end of October. 



They were able to follow the changes of 

 its size and shape, its division into several 

 parts by the large black band, and to estab- 

 lish further the persistence of certain parts 

 isolated from the greater body. They also 

 observed the changes of color which took 

 place in the surrounding dark regions. 

 Plate II., page 46, gives the definitive re- 

 sults of that investigation, which, in com- 

 parison with similar work hitherto, suffi- 

 ciently shows the superiority of the means 

 with which Mars has been visually studied 

 at Flagstaff. 



I may be permitted to express here 

 the conviction that it is by the exact and 

 persevering study of the polar spots of 

 Mars that we shall some day arrive at a 

 sound knowledge of the physical nature of 

 that planet, and the interpretation of its 

 singular phenomena. I shall even venture 

 to say that if the southern cap is very instruc- 

 tive in that respect, the northern cap is still 

 more so. In fact, the latter develops to a 

 large extent over the regions of a yellow 

 color which it is customary to call conti- 

 nents. The obscure band which reaches to 

 its edge has a direct relation to the system 

 of canals and lakes surrounding it. In the 

 same measure as the white spot diminishes 

 under the influence of the solar rays, there 

 take place in the neighboring regions very 

 considerable changes, the connection of 

 which with the successive phases of the cap 

 is evident. The facts that I was able to 



