On the east, some of them barred with luminous network the _Mare Nubium_ and even the _Mare Humorum_.
The most puzzling feature of these glittering streaks was that they ran their course directly onward, apparently neither obstructed by valley, crater, or mountain ridge however high.

They all started, as said before, from one common focus, _Tycho's_ crater.

From this they certainly all seemed to emanate.

Could they be rivers of lava once vomited from that centre by resistless volcanic agency and afterwards crystallized into glassy rock?
This idea of Herschel's, Barbican had no hesitation in qualifying as exceedingly absurd.

Rivers running in perfectly straight lines, across plains, and _up_ as well as _down_ mountains! "Other astronomers," he continued, "have looked on these streaks as a peculiar kind of _moraines_, that is, long lines of erratic blocks belched forth with mighty power at the period of _Tycho's_ own upheaval." "How do you like that theory, Barbican," asked the Captain.
"It's not a particle better than Herschel's," was the reply; "no volcanic action could project rocks to a distance of six or seven hundred miles, not to talk of laying them down so regularly that we can't detect a break in them." "Happy thought!" cried Ardan suddenly; "it seems to me that I can tell the cause of these radiating streaks!" "Let us hear it," said Barbican.
"Certainly," was Ardan's reply; "these streaks are all only the parts of what we call a 'star,' as made by a stone striking ice; or by a ball, a pane of glass." "Not bad," smiled Barbican approvingly; "only where is the hand that flung the stone or threw the ball ?" "The hand is hardly necessary," replied Ardan, by no means disconcerted; "but as for the ball, what do you say to a comet ?" Here M'Nicholl laughed so loud that Ardan was seriously irritated.
However, before he could say anything cutting enough to make the Captain mind his manners, Barbican had quickly resumed: "Dear friend, let the comets alone, I beg of you; the old astronomers fled to them on all occasions and made them explain every difficulty--" -- "The comets were all used up long ago--" interrupted M'Nicholl.
-- "Yes," went on Barbican, as serenely as a judge, "comets, they said, had fallen on the surface in meteoric showers and crushed in the crater cavities; comets had dried up the water; comets had whisked off the atmosphere; comets had done everything.