636 



SCIENCE. 



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



would be to give up the doubtful objects, 

 and to make as complete and exact a study 

 as possible upon those canals best known 

 and most easily observed, following with- 

 out interruption the variations of their 

 aspect and of their course, and basing de- 

 ductions upon precise measures. Precise 

 measures ! the thing most necessary and at 

 the same time the most difficult, which 

 ought to receive more attention from skilled 

 observers. 



The proportion of new discoveries at 

 Flagstaff on the small dark spots called 

 lakes (Mr. Lowell's oases') is relatively still 

 more considerable. Prior to the opposition 

 of 1894 ten to twelve of these formations 

 were known. Mr. Lowell gives a cata- 

 logue of more than forty of them. He 

 has shown that in most cases these oases 

 are arranged in regular series on the 

 routes of the longer canals. It is quite 

 probable that minute dark spots, more or 

 less readily visible, must exist at all points 

 of intersection of any two canals. 



There is still another class of objects on 

 which the Flagstaff observers have insti- 

 tuted the first thorough research. These 

 are the black lines which furrow the darker 

 portions of the surface of Mars and are 

 ordinarily called the seas. Some lines of 

 that sort had been noticed before, and even 

 a form of gemination had been established 

 for two of them.* In general, previous 

 observers had believed that they saw here 

 lines of the greatest faintness rather than 

 true canals ; in only a very few special 

 cases did they succeed in tracing the two 

 edges distinctly. At Flagstaff these lines 

 have been observed and reproduced with 

 much care by Mr. Douglass, who seems to 



*See on my map of 1882 the two parallel lines 

 ■wbich include between them the large island called 

 Noaehis ; one of these is named Prasodes on CeriTlli's 

 map. See also the two lines which flank the right 

 side of Sijrtis Xagna on my drawing of June 20, 1890, 

 published by Flammarion {La Planete 3Jars, p, 476). 



have a very sensitive and well-trained eye 

 for that sort of objects. From measures of 

 position angles he traced on two maps their 

 course in the dark regions of the planet and 

 their connection with the canals of the yel- 

 low region. See plates XII and XIII. 



The third chapter of the volume is also 

 the work of Mr. Douglass, and deals with a 

 class of observations which are almost un- 

 known, except for some essays in this direc- 

 tion at Nice and at the Lick Observatory 

 in 1890 and 1892. I refer to the irregu- 

 larities which have been very often noticed 

 at the terminator, i. e.,on the line which at 

 any instant separates the obscure from the 

 illuminated hemisphere. These are very 

 evident when the phase is considerable, 

 near the quadratures. In by far the greater 

 majority of cases these irregularities are 

 merely optical illusions caused by the dif- 

 ferent proportion of the oblique solar illu- 

 mination returned to us in the different 

 regions traversed by the terminator. But 

 there seem to be certain of these irregular- 

 ities which can only be explained by the 

 presence of elevations or depressions on the 

 surface of Mars. Still others seem to de- 

 pend upon the presence of very high clouds. 

 These investigations are of much interest, 

 not only from their possible bearing on the 

 topography and orography of Mars, but also 

 from the point of view of the physical his- 

 tory of the planet and its atmosphere. 



The work is enriched by a large number 

 of drawings of Mars, some of which are 

 really excellent even from an artistic point 

 of view. See especially plates I and IV. 

 We have seen nothing as beautiful since 

 the drawings made by Mr. Green on his 

 expedition to Madeira in 1877. We can 

 recognize here not only the geometrical con- 

 figurations and the varieties of light and 

 shade, but we can also get some idea of the 

 magnificent coloration observed on the 

 planet. 



The chart placed at the end of the vol- 



