286 Lunar Mountains Tyclio^ Pictet, and Saussure. 



crater C, whose cavities are connected among themselves : still smaller ones 

 are in the neighbourhood, and somewhat further off is the crater ^, of a re- 

 gular and very distinct form. We may say that this region swarms with 

 craters, some of the diameters of which do not appear to exceed half a se- 

 cond, and which are notwithstanding upon the whole more visible than the 

 intervening mountains : these are seldom 300 feet high, and are chiefly dis- 

 tinguished by the total absence of more elevated mountains.* 



It cannot be doubted that Tycho is the point of departure of a system of 

 rays, which occupies in its whole extent at least a quarter of the visible 

 surface of the moon. • » • The bands are so approximated towards 

 the west, that they unite in an almost continued surface over the south-west 

 quadrant, so that it is difficult to perceive any difference ; and the dazzling 

 brightness in no slight degree increases the difficulty of making investiga- 

 tions respecting this region. They are lost towards the margin. These 

 bands become visible as soon as the sun rises from 20° to 25° above the 

 horizon, whether Tycho itself is illuminated or not, and they disappear 

 when the sun redescends from them to the same extent. A portion of the 

 more luminous, especially those which are situated upon a dark basis, are 

 still for a long time visible, but none at the rising and setting of the sun. 

 At the same time some may be distinguished in the obscure part of the 

 moon by the simple effect of the illumination from the earth. 



It is only during the full moon that we can see the radiated system com- 

 pletely, and it is best distinguished when the latitude ofthe moon is northwards. 

 So soon as the shadows of the mountains begin to appear in any region, the 

 bands disappear, and conversely. To such an extent is this true, that so 

 Boon as the system of bands appear, you can no longer detect the slightest 

 traces of the larger and highest annular mountains, or even mountain- 

 chains, even when you are intimately familiar with their exact position. 

 Still, however, very feeble traces of some of them may be discovered, such 

 as Saussure, Piccolomini, and Lindenau, as well as Mount Altai, and some 

 other neighbouring objects; but for this first-rate instruments, and a very 

 favourable state of the atmosphere are required. There are also some 

 small craters (small in number, and generally not remarkable), which are 



• Though the mountain which is called Deluc is somewhat more distant from 

 Tycho, to the south of Saussure, it may be interesting to supply a short descrip- 

 tion. It is an annular mountain, of a circular form, with a diameter oi six Ger- 

 man miles, enclosing a small central mountain. Its western margin, which is 

 the most elevated, does not exhibit a distinct peak, as does the eastern, which 

 is broader withal. Two still smaller annular mountains, which are close together, 

 d and H (the latter situated in 54° 8' south latitude, and 2° 32' east longitude), 

 are symmetrically situated to the south and north, and the latter has a central 

 mountain. The point A:, situated in the neighbourhood, is the only surface which 

 appears obscure at the time of full moon, and consequently remains visible even 

 then, when its locality is well known ; the point m also remains visible like a 

 faint ring of light : every thing else disappears. This region is to be found near 

 the first meridian of the moon, passing from the centre to the poles. The cra- 

 ter Deluc E is situated towards the south-east limit of this region, in 66°20' lati- 

 tude, and 5° 31' longitude. The whole of this region exhibits few traces of past 

 ijommotions, and nevertheless presents a very considerable luminous brightness. 





