69 



alteiward niuioiinoed that at eertain seasons these canals appeared to be 

 doul»led, and tlie same thing has been seen many times since, although as 

 yet there is no really probable explanation offered. It has been supposed 

 to lie an optical effect by some, and due to atmov^pheric causes by others, 

 and by some it is thought that the canal is really douI)le. This doubling 

 is shown in the drawing made on April 7. 



As the rotation period of Mars is about thirty-nine minutes longer than 

 our day, by looking at the planet at the same hour on successive nights 

 we will see any particular marking shifted to the right from the center 

 by about IK degrees Martian longitude for each night. We are therefore 

 able, in the course of about thirty-eight days, to view the whole surface 

 by looking for a short time each night, and the rotation is sufficiently 

 rapid so that even in the course of three or four hours tlie amount of 

 new detail brought into view is large.' 



In the drawings of February 15 the most conspicuous part of the whole 

 dislv is the great northern ice cap with a large dark area liordering it. 

 The dark band of color across the southern part of the planet is a portion 

 of that great area, supposed at one time to be water, and near the center 

 of the disk are two of the so-called canals, which, on this night, could 

 be followed only for a short distance. 



In all these drawings the contrast lietween the light and darlv parts of 

 the planet has been drawn greater than it really appears, so that the 

 drawing would reproduce better. The outlines have been made distinct or 

 hazy as they appeared, but the dark parts of the planet are not so dark 

 generally as shown here. 



By comparing the drawings of February 15 and those of February 20. 

 the eastward drift of about ten degrees per day, mentioned above, has 

 brought into view a very dark and conspictious marking which will be 

 found a numlier of times in the drawings of later date and which was 

 always connected with the dark area about the pole by a well defined but 

 irregular dark mark liest shown in the draAvings of the early part of April. 

 This was the first real detail ever seen on the planet and was drawn by 

 Huyghens in 1(>.19. It has probably received more attention from observers 

 than any other part of the planet. This dark line, with many more, from 

 the polar seas leading toward the equator naturally suggests that the so- 

 called canals do really carry away the water resulting from the melting 

 snow. As they are about thirty miles wide, it has been suggested as 

 more probable tliat they are really strips of vegetation bordering the 

 5— Academy of Science. 



