April, 1904.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



^1 



that though the central regions of the disc are as " rough 

 and mountainous as that near the pole " they are very much 

 darker. It is hardly the fact that the equatorial regions 

 are as rugged as those of the North Pole, hut when we 

 compare the equatorial regions with the polar under the 

 same conditions of foreshortening as well as of illumination 

 the latter have no evident superiority in brightness. It 

 is abundantly clear why the regions near the edge of the 

 disc, whether polar or equatorial, appear the brightest, 

 for it is just here that the darker valleys are concealed 

 from us and that the steep mountain slopes are presented 

 to the fullest advantage. 



The question as to whether there are anywhere upon 

 .the moon deposits of snow is too large a one to be settled 

 by an appeal to the evidence which even so grand and 

 extensive a formation as the Apennines and their high- 

 lands can afTord, but so far as they are concerned the 

 verdict would clearly seem to be in the negative. It must 

 always be difficult to distinguish upon the moon betw^een 

 changes which are simply due to changed illumination, 

 and therefore which are apparent only, and changes 

 which are real but are strictly seasonal, for the period of 

 both will be the same. But in this particular region both 

 theory and observation seem to unite in discountenancing 

 the idea of snowfall and in ascribing the apparent changes 

 in the brightness of the Apennine highlands purely to 

 the varying incidence of light on surfaces of different 

 reflective power. 



The CaLrvQLls of Ma^rs. 



By \V. F. Denning, F.R.A.S. 



Recent observations and discussions in reference to the 

 canals of Mars have been very important and will be 

 the means of clearing up doubtful points and putting our 

 knowledge of the planet's surface configuration on a well- 

 assured basis. The fact that many of the spots on I\Iars 

 represent real features give them a special interest, for the 

 other large planets of our system appear to be too densely 

 involved in atmospheres to exhibit the material conforma- 

 tion of their globes. 



Schiaparelli discovered the canaliform aspect of ;\lars 

 in 1877, and the general correctness of the Italian astro- 

 nomer's work has been affirmed by many of the leading 

 planetary observers in subsequent years. But the path 

 of the pioneer is difficult and apt to carry one a little 

 astray through its general direction may be accurate 

 enough, Schiaparelli has not been successfully followed 

 in all the details included in his charts of Martian topo- 

 graphy, nor has the doubling of many of the canals been 

 corroborated. But apart from the latter peculiarity his 

 delineations form the best working basis for present 

 observers, and carry us tar beyond the charts of Green, 

 whose well-executed drawings are marred by the fact 

 that he was over-scrupulous as to the insertion of details 

 not prominently distinguishable. 



Schiaparelli has no doubt delineated the canals undei 

 aspects too straight, hard, and uniform. P'or the most 

 part the telescope displays them as really faint pencil- 

 like streaks or veins, knotted with darker regions and 

 by no means of equable width or even tone. Though 

 classed under one name and drawn in a uniform way 

 they certainly represent very dissimilar objects. 



Some of the canals are due to contrast, and r- 

 apply to the boundaries between dusky areas toned a 

 little more deeply than the outlying parts of tlie ruddy 

 surface. 



Others are pretty consistent with their title, being 



formed of streaks apparently connectin , i%nown 



spots, and sometimes meandering over extensive tracks 

 of the surface. 



Others again are composed of small irregular con- 

 densations, lying approximately in rows and roughly 

 blended together under the aspect of bands in which 

 much detail may be momentarily glimpsed. With ordi- 

 nary telescopic power, however, tlieir general appearance 

 on the small disc is that of streaks or canals, and tiie 

 observer (igures them as such, being unable to satisfac- 

 torily define their structure in detail. 



In Marcii, 1903, I i)egan a series of careful observa- 

 tions of Mars with a lo-inch reflector. I'avourahle 

 weather during tlie ensuing two months enabled me to 

 examine the planet on 26 nights, when 36 drawings were 

 made. On the first few nights 1 detected some of the 

 canals under absolutely certain characters. .\ consider- 

 able number of those shown in Schiaparelli's charts were 

 identified, and the result of my scrutiny was to prove the 

 general correctness of his drawings. Hut I utterly failed 

 to recognize the supposed double canals. To my eye, 

 the lines were invariably single under the highest powers 

 I could effectively apply, and I am bound to conclude 

 that the gemination is not a real feature. 



Mars in the Spring of 1003. LonifUude, 2O5 . 

 io°inch Kefltctor. Powers, 312 and 375. 



During my observations several striking changes were 

 remarked in prominent objects, and these were probably 

 occasioned l)y atmospheric movements on tl^e surface of the 

 planet. The presence of clouds or obscuring vapours 

 must, however, havealTected relatively small regions, for the 

 markings were usually visible from night to night under 

 similar aspects, allowance being made for the variable 

 definition. 



The white spots formed striking features, and especially 

 so when on or near the edge of the disc. They appeared 

 to be equally as permanent as the dark markings. 



From observed transits of the Syrtis Major, compared 

 vith some I obtained with a 4y-in. refractor in February, 

 . ^69, I determined the rotation period as 24h. 37m. 22-7S. 

 from 12,135 rotations. 



There are really many distinctions in the canal-like 



markings ; some of them are quite broad and diffused 



hadings, while others are narrow-, delicate lines. The 



