OF THE SURFACE OF THE MOON. 
339 
contrasted in brightness with the neighbouring surfaces, being easily traceable, if conti- 
nuous, where much broader tracts of a square or circular figure cannot be discerned. 
This is familiar to persons who trace by the eye the far extended narrow telegraph wire. 
But more than this. The rills are, under favourable lights, seen to be really fissures with 
one dark and one enlightened side — deep dark fissures. Bills of this remarkable cha- 
racter do not appear to be branched ; and in this respect the long rill of Hyginus, marked 
on Madler’s map for ninety-two miles, may be compared with the great North of 
England dyke, which extends from Teesdale to near the Peak on the coast of Yorkshire, 
seventy miles, without a branch. Contraction, rather than violent movement of the 
moon’s crust, seems to suit best the facts observed ; and the same explanation may be 
fairly applied to most of the fissures filled with whinstone in the coalfields of Durham 
and Northumberland. Still the straight rill near Tebit (called the Kailroad), nearly on 
the central meridian of the moon, bears the appearance of dislocation in the shadow 
thrown by one side. 
The rill which descends from Herodotus is of a different but equally remarkable cha- 
racter. Parting from that dark crater — full perhaps of augitic compounds, in strange 
contrast with its neighbour Aristarchus, which shines as if formed of white trachyte — 
the rill takes a winding course with some irregularity of width and appearance, till it 
opens into what resembles an old delta, or dried gulf, margined by cliffs, and undulated 
by recesses and promontories. The delta-like space is uneven, like the bed of the 
German Ocean. Still, there are appearances in this seeming valley and outlet to an 
ancient sea, which can hardly be reconciled to the conjecture. The rill has no branches ; 
in the middle of its course is an oblong crater which makes a part of the seeming chan- 
nel ; and thus this falls into the general rule which makes the rills dependent on the 
craters, so as to pass commonly, but not always, from one crater to another, and often 
to traverse them through the ring and athwart the interior space (Plate XVII.)*. 
A very different class of phenomena may also be referred to some change of dimen- 
sions or some displacement of masses affecting large surfaces of the moon. These are 
the light-streaks which, from Tycho in particular, radiate, like false meridians, or rather 
like meridians true to an earlier pole of rotation. Other light-streaks pass off from 
Copernicus and Kepler, and several other mountains, but none are comparable to those 
from Tycho. There is this singularity about them ; they are most distinctly visible in 
the full moon, and for some days before and after that phase. When the light falls at 
a low angle on the part of the moon’s disk where one or more of these rays exist, they 
do not appear ; as the sunlight strikes at higher and higher angles they come out bright 
and clear, again vanishing as the lunar evening comes on. 
By the strictest examination these luminous bands are found to have no projection 
above and no depression beloAv the surface, no shadow on either boundary. They can be 
traced across what look like seas, and equally traverse the crateriform mountains, con- 
tinuously ; sometimes branching, often varying in breadth. On a first view they seem 
* See additional notices in the Supplement. 
