TRANSACTIONS OF THE SECTIONS, a, 
in a rotating circular plate, which is prevented from becoming inconyeniently heated 
by a layer of plaster of Paris on its first surface, and by a coating of enamel on the 
brass plate on which it rotates. The eye-lenses and dark glasses are also arranged 
in rotating wheels. : 
By the use of the smallest apertures in the diaphragm-plate, the middle, or 
umbra, of large solar spots may be advantageously scrutinized, all the rest, even 
the penumbra of the spot itself, being excluded from view. It was in this way 
that the inventor discovered the irregular illumination and cloudy appearance of 
the umbra (which was previously supposed to be black, and probably the body of 
the sun itself), and the existence, in most of the larger and more symmetrical spots, 
of a small well-defined portion in which no light at all could be seen, and to which 
alone the term nucleus (often erroneously applied to the whole of the wnbra) ought 
to be restricted. This is the more important, as the inventor has arrived at the 
conclusion that the existence or non-existence of this entirely black nucleus forms 
an obvious distinction between two classes of solar spots, whose origin is of a very 
different kind. 
This eyepiece is also of great utility in several other species of observation ; as, 
e. g.,in the scrutiny of minute and delicate portions of the moon’s surface, while the 
eye is relieved by the exclusion of all the rest from the field of view; in observing 
lunar occultations, and the eclipses of Jupiter’s satellites, and in examining the 
immediate vicinity of planets for faint satellites, and of bright stars for minute com- 
panions. The diameters of the apertures in the diaphragm-plate vary from 0:5 to 
about 0-01 of an inch. As there is some difficulty in cleaning out the smallest of 
these without injuring it as a point of a fine needle might do, it may be well to 
mention that the inventor has found the best instrument for this purpose to be a 
ceat’s whisker, 
On the Lamar “ Mare Smythii,” the walled Plain “ Rosse,” the “ Perey Moun- 
tains,” and the newly named Craters, “ Phillips,” “ Wrottesley,” ‘“ Cheval- 
her,” and “ Piazzi Smyth.” By Dr. Lex, F.R.S. 
The “ Mare Smythii” *.—This interesting portion of the moon’s surface was first 
observed with sufficient care, and delineated accurately, by Schréter in 1792, Sept. 30, 
twenty-two hours after full moon. T. Mayer and Cassini had represented in its locality 
a long grey streak. Schréter’s drawing, in the main, is executed with ereat fidelity, 
and represents all the principal features of the Mare, as well as some interesting 
craters east of it. In this respect, as well as in a portion of the eastern rim, it is 
closely in accordance with a drawing made by Mr. Birt on the 30th of J uly, 1863, 
when the terminator bisected the surface of the Mare. Mr. Birt also had an 
cpprnnity, on the 25th of November, 1863, of verifying in almost every particular 
chroter’s delineation. Schréter designated this extensive lunar plain “ Abraham 
Gotthelf Kistner,” and delineated and described two somewhat extensive depres- 
sions eastward of the southern part of the Mare, It would appear from Beer and 
Madler’s large map that these great selenographers had but imperfectly seen this 
fine Mare, nearly equal in extent to the Mare Crisium, for they describe “Kistner” 
as extending like a sea from —2° to— 9° south latitude; and that it is almost 30 Ger- 
man miles in length, while they make the Mare Crisium 61 German miles long. They 
give on their map a dark plain even smaller than that described above, and which, 
rom a careful comparison of the drawings now in existence, appears to be the 
eastern portion only of the southern part of Schriter’s “Kistner.” Schroter’s 
delineation being thus so considerably reduced by Beer and Miidler, it becomes 
quite impossible to identify their “Kistner” with the Mare in question. Accord- 
ingly when, on August 20th, 1861, it was seen by Mr. Birt in the immediate 
neighbourhood of the terminator, the observation assumed the character of a dis- 
peers in fact, the mutilation of this fine plain by Beer and Miidler clearly renders 
the observation of Mr. Birt a rediscovery of the true “Kistner ” of Schroter, while 
the position of one of the depressions east of its southern portion is so nearly 
* The name “ Smythii” is given to this Mare in commemoration of the extensive and 
lone labours of the accomplished and gallant admiral, the author of the ‘ Celestial 
'ycle.’ 
