518 REPORT—1868. 
combination of these perceived relations. My eye, which has undergone an 
operation for cataract, will no longer permit me to make accurate and special 
continuous observations; yet on the 10th of May, 1867, I attempted an 
observation of the crater Linné in the heliometer of the Observatory at Bonn. 
I found it shaped exactly, and with the same throw of shadow, as I remem- 
ber to have seen it in 1831. The event, of whatever nature it may have been, 
must have passed away without leaving any trace observable by me. I de- 
sire now to recommend to moon-observers a hitherto little considered subject, 
and one formerly very erroneously interpreted—the “ straits” of light which 
only show themselves in high sun illumination ; they make a show on Heye- 
lius’s map, and even much later, as Montes, Myconius, Eryx, Crates, Hereus, 
Sepher, and Seir, while still nothing is certain about them but that they are 
by no means elevations. Ridges of only 50 feet high are yet to be recognized 
through their shadow near the light edges, whilst these straits never show 
the smallest shadow, and vanish in the vicinity of the light edges. Their 
effect is that we perceive in the full moon but very little of what is seen in 
the quadratures, and especially near the light edges. Most probably it is only 
a very great capability of reflection of the ground by the high position of the 
sun and referrible to internal causes. They proceed in a radiating manner 
from single bright ring-mountains, especially from Tycho, Copernicus, Kepler, 
Byrgius, Aristarchus, and Olbers; from some other ring-mountains only 
single straits are proceeding on one side, as with Menelaus and Proclus. 
By a superficial observation they may easily be confounded with the moun- 
tain veins, and so much the more as these latter have often their origin at 
ring-mountains; but an attentive observer will easily remark essential dif- 
ferences between both appearances. I have endeavoured in my moon map to 
represent them; other observers (with the exception of those early ones who 
have explained them erroneously) have not come to my knowledge—I mean 
as to whether they have made research respecting changes which may occur 
in them. ‘The easiest to observe is the light strait which divides the M. Sere- 
nitatis almost equally in halves; still there is another circumstance which 
recommends it to a closer inquiry, viz. because it is visible almost up to the 
light edge. I have sometimes still observed traces of the N.W. part of the 
strait when that of the S.E. was yet covered in night, since none of the other 
straits admitted so long a visibility; I have examined it several times for traces 
of shadow, but never perceived the smallest. Lastly, I would point out the 
rills of the moon’s surface as objects whose visibility probably does not de- 
pend only on our atmosphere, but is to be referred to real changes; thus I have 
sought for two long years in vain for the 8.W. continuation of the Ariadseus 
rill (though its existence came to my knowledge from other quarters) till it 
came unexpectedly to my view in 1833—certainly a most delicate object. It 
will always be advisable to observe on the same evening, not merely a single 
rill, but many somewhat similar ones; for, as the earth’s atmosphere must 
exercise a like effect upon them all, so would a perceptible variation present 
us with a hint for further investigations. 
Wishes and propositions, with the recollections of former years, are all 
which I am now able to offer. May they be an inducement to younger and 
more vigorous observers to draw new and fructifying facts to the light of our 
science! and may our satellite, after the monstrous fables which for almost 
the space of many thousand years have gained credence respecting it, now 
begin, not only by its course, but also by its natural constitution, to permit us 
to pierce deeper into the secrets of the fabric of the universe! 
