PORTION OF THE COSMOS. THE PLANETS. 365 



An exceedingly curious and enigmatical phenomenon in 

 the surface of our satellite, and one which seems to belong 

 to an optical effect ot luminous reflection, and not to a hyp- 

 sometric difference, is presented by the narrow streaks of 

 light which disappear in an oblique illumination, and, con- 

 trary to the lunar spots, are most visible in the full moon. 

 These streaks form radiating systems. They are not lines of 

 mountains, they do not cast any shadows, and they run in 

 uniform intensity of light from the plains to elevations 

 twelve or thirteen thousand feet and upwards. The most 

 extensive of these radiating systems is that which proceeds 

 from Tycho, and in which more than a hundred streaks of 

 light, mostly of several miles in breadth, can be distin- 

 guished. Similar systems, surrounding Mounts Aristarchus, 

 Kepler, Copernicus, and the Carpathians, are almost all 

 connected with each other. It is difficult to conjecture 

 from analogy or induction what is the particular alteration 

 of surface which occasions these bright shining bands, 

 radiating from particular annular mountains. 



The circular type which we have already noticed as 

 prevailing almost everywhere upon the Moon's surface, (in 

 the wall-surrounded plains which often inclose central 

 mountains, and in the great annular mountains and their 

 craters, of which 2 have been counted in Bayer, and 33 in 

 Albategmus, crowded closely together) gave occasion to 

 the profound thinker, Robert Hooke, to seek for the cause 

 of this phenomenon in the reaction of the interior of the 

 Moon against its exterior ; or, as he expressed it, as " the 

 effect of subterranean fires and elastic vapours breaking 

 forth even to ebullition, sending up to the surface bubbles 

 or blisters." Experiments by boiling thick calcareous solu- 



