232 



LOWELL — A REOGR APH Y . 



[April 4, 



is of their essence. But the observations necessary to its apprecia- 

 tion are not easy. Probably even to-day not above a dozen persons 

 have seen the canals well enough to make their opinion on the sub- 

 ject of weight, but all who have done so agree in their dictum. 



12. As with the first and second periods, so with the second and 

 third there was a transition state between the two. What Dawes 

 had done for the first gap, VV. H. Pickering and the Lick observers 

 did for the second. In 1892, at Arequipa, Pickering found irregu- 

 larly narrow markings in the midst of the then called seas, and the 

 Lick observers detected ^^ streaks " in the same regions. These 

 played much the same part, though in the case of the Lick ob- 

 servers much more, to subsequent work that the Dawes' markings 

 had to Schiaparelli's, so far as ''canal " detection is concerned. 



13. For in 1894 Mr. Douglass at Flagstaff found that the irreg- 



FiG. 10. 



Map of Lowell, 1896-97. 



ular lines of Pickering and the streaks of the Lick observers were 

 foreshadowings of something much more peculiar. He found that 

 a system of lines of the startlingly regular character which gives to 

 the ''canals" their technical interest, overspread the whole of the 

 great southern dark areas. Thus the third period marks the detec- 

 tion of "canals" in the dark regions, and from that a complete 

 change in the character of the seas, already in part so ably detected 

 by Pickering. Furthermore, the network of each system showed 



