NOTES ON MARS. 167 



lines and spots we find in the faint markings of Mars might be merely 

 the easiest form in which, with our present optical means, we could be 

 cognizant of its real features. This latter treatise elicited replies from 

 Schiaparelli and Flammarion, but their arguments in favor of the 

 physical existence of the markings as such, and of actual changes tak- 

 ing place in them, are not altogether conclusive. Signor Cerulli's 

 observations during the last opposition have confirmed him in the 

 belief that the markings are optical, and his new report^ is substan- 

 tially a full exposition of his theory. These observations extended 

 from August, 1898, to March, 1899, and were made with a 15i-inch 

 Cooke equatorial, with powers of 100 and 500, always without stops or 

 colored screens, the object being not to get sharp definition of any 

 special feature, but as complete a picture as might be of all the phe- 

 nomena. The author shows what is the explanation, on his theory, of 

 the features seen and their apparent variations, and brings forward 

 ingenious and novel arguments to prove his case. 



It must be remembered that in a bird's-eye view of a world 

 some 40,000,000 miles away all we can take note of are contrasts 

 in tone or color, while the real contour of objects is masked or 

 invisible. Small or faintly shaded objects, invisible singly, will 

 produce an efl'ect, if close together, of one large mass, and from 

 pur inability to see the irregularity of their grouping will ap- 

 pear as round spots or long streaks. But conditions of seeing 

 vary enormously on Mars, according to its distance and position 

 and the changing illumination of its disk, not to speak of varia- 

 tions in ourselves, our atmosphere, and our instruments. The con- 

 trasts, therefore, will vary, more detail will sometimes be seen in 

 the patches and streaks, fainter markings at their edges will appear 

 and disappear, altering their outline and extent. The hazy aspect of 

 Schiaparelli's canals may thus be a nearer approximation to reality 

 than the sharply defined, and the doubling may be due to disappear- 

 ance of faint shadings between more easily grasped boundaries. That 

 the canals were discovered after the opposition of 1877, being only sus- 

 pected during the most favorable period, that they are sharpest with 

 colored screens and comparatively small apertures, while in the great 

 Lick and AVashington telescopes they have been seen either as few 

 diffused markings or not at all, suggest that the fine lines are simply 

 a mode under which faint markings may present themselves to imper- 

 fect vision. There is undoubtedly truth in the apparent paradox that 

 greater distinctness comes with poorer vision, for in the best moments 

 the eye dimly perceives, even where it can not grasp, divisions in 

 simple masses, curves, and blurring in narrow lines,- indeterminate 

 shadows in clear spaces. 



^Nuove osservazioni di ]Marte: Saggio di una interpretazione ottica delle sensazioni 

 areoscopiche. ByY. CeruUi. CoUurauia, 1900. 



