296 POPULAR SCIENCE MONTHLY. 



inhabitants have found it necessary to economize to the utmost 

 whatever stock there may be of this most necessary element. The 

 observations at Flagstaff tend to show that the dark lines on Mars 

 mark the course of the canals by which the water melted in sum- 

 mer in the arctic regions is conducted over the globe to the tracts 

 where the water is wanted. Not that the line as we see it repre- 

 sents actually the water itself; the straight line so characteristic 

 of Mars's globe seems rather to correspond to the zones of vegeta- 

 tion which are brought into culture by means of water that flows 

 along a canal in its center. In much the same way would the 

 course of the Nile be exhibited to an inhabitant on Mars who was 

 directing a telescope toward this earth: the river itself would not 

 be visible, but the cultivated tracts which owe their fertility to 

 the irrigation from the river would be broad enough to be distin- 

 guishable. The appearance of these irrigated zones would vary, 

 of course, with the seasons; and we observe, as might have been 

 expected, changes in the lines on Mars corresponding to the changes 

 in the seasons of the planet. 



A noteworthy development of astronomy in the last century 

 has been the erection of mighty telescoj^es for the study of the 

 heavens. It m.ust here suffice to mention, as the latest and most 

 remarkable of these, the famous instrument at the Yerkes Observa- 

 tory, which belongs to the University of Chicago. Just as the 

 century is drawing to its close, the Yerkes telescope has begun to 

 enter on its sublime task of exhibiting the heavens under greater 

 advantages than have ever been previously afforded to any astrono- 

 mers since the world began. 



The University of Chicago having been recently founded, it 

 was desired to associate with the university an astronomical ob- 

 servatory which should be worthy of the astonishing place that this 

 wonderful city has assumed in the world's history. Mr. Yerkes, 

 an American millionaire, generously undertook to provide the cost 

 of this observatory. Two noble disks of glass, forty inches in 

 diameter, were produced at the furnaces of Messrs. Mantois, in 

 Paris; these disks were worked by Mr. Alvan Clark, of Boston, 

 into the famous object glass which, weighing nearly half a ton, has 

 now been mounted in what we may describe as a temple or a palace 

 such as had never been dreamed of before in the whole annals of 

 astronomy. 



Perhaps if we could now place the science of the nineteenth 

 century in its proper perspective the most remarkable discovery 

 which it contains would be that of the planet Neptune. Indeed, 

 the whole annals of science present no incident of a more dramatic 

 character. 



